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 $228.48   6.437%   $243.1873   $243.19   $243.20   $243.20  
  Purchase #2 $183.55   12.783%   $207.0132   $207.01   $207.00   $207.00  
  Purchase #3 $191.39   5.185%   $201.3136   $201.31   $201.30   $201.30  
  Purchase #4 $64.42   7.233%   $69.0795   $69.08   $69.10   $69.10  
  Purchase #5 $205.81   13.129%   $232.8308   $232.83   $232.85   $232.80  
  Purchase #6 $77.92   13.455%   $88.4041   $88.40   $88.40   $88.40  
  Purchase #7 $155.34   11.239%   $172.7987   $172.80   $172.80   $172.80  
  7 purchase totals = $1,106.91       $1,214.6272   $1,214.62   $1,214.65   $1,214.60