Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.58   11.339%   $232.2309   $232.23   $232.25   $232.20  
  Purchase #2 $241.46   11.135%   $268.3466   $268.35   $268.35   $268.30  
  Purchase #3 $139.30   7.793%   $150.1556   $150.16   $150.15   $150.20  
  Purchase #4 $165.57   8.862%   $180.2428   $180.24   $180.25   $180.20  
  Purchase #5 $111.92   13.574%   $127.112   $127.11   $127.10   $127.10  
  Purchase #6 $147.62   8.600%   $160.3153   $160.32   $160.30   $160.30  
  Purchase #7 $203.84   7.155%   $218.4248   $218.42   $218.40   $218.40  
  7 purchase totals = $1,218.29       $1,336.8280   $1,336.83   $1,336.80   $1,336.70