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 $65.34   12.384%   $73.4317   $73.43   $73.45   $73.40  
  Purchase #2 $224.86   8.261%   $243.4357   $243.44   $243.45   $243.40  
  Purchase #3 $177.80   12.466%   $199.9645   $199.96   $199.95   $200.00  
  Purchase #4 $88.75   5.495%   $93.6268   $93.63   $93.65   $93.60  
  Purchase #5 $83.74   4.579%   $87.5745   $87.57   $87.55   $87.60  
  Purchase #6 $155.94   10.316%   $172.0268   $172.03   $172.05   $172.00  
  Purchase #7 $67.56   7.449%   $72.5925   $72.59   $72.60   $72.60  
  7 purchase totals = $863.99       $942.6525   $942.65   $942.70   $942.60