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 $170.58   6.273%   $181.2805   $181.28   $181.30   $181.30  
  Purchase #2 $186.92   7.745%   $201.397   $201.40   $201.40   $201.40  
  Purchase #3 $72.56   6.821%   $77.5093   $77.51   $77.50   $77.50  
  Purchase #4 $83.29   12.526%   $93.7229   $93.72   $93.70   $93.70  
  Purchase #5 $180.91   11.694%   $202.0656   $202.07   $202.05   $202.10  
  Purchase #6 $17.57   6.130%   $18.647   $18.65   $18.65   $18.60  
  Purchase #7 $114.94   12.479%   $129.2834   $129.28   $129.30   $129.30  
  7 purchase totals = $826.77       $903.9057   $903.91   $903.90   $903.90