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 $150.45   8.355%   $163.0201   $163.02   $163.00   $163.00  
  Purchase #2 $238.28   11.595%   $265.9086   $265.91   $265.90   $265.90  
  Purchase #3 $86.93   10.474%   $96.035   $96.04   $96.05   $96.00  
  Purchase #4 $87.78   6.146%   $93.175   $93.18   $93.20   $93.20  
  Purchase #5 $149.98   12.752%   $169.1054   $169.11   $169.10   $169.10  
  Purchase #6 $107.65   9.431%   $117.8025   $117.80   $117.80   $117.80  
  Purchase #7 $204.56   6.109%   $217.0566   $217.06   $217.05   $217.10  
  7 purchase totals = $1,025.63       $1,122.1032   $1,122.12   $1,122.10   $1,122.10