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 $30.68   9.652%   $33.6412   $33.64   $33.65   $33.60  
  Purchase #2 $173.25   9.743%   $190.1297   $190.13   $190.15   $190.10  
  Purchase #3 $89.26   11.437%   $99.4687   $99.47   $99.45   $99.50  
  Purchase #4 $213.95   7.755%   $230.5418   $230.54   $230.55   $230.50  
  Purchase #5 $135.59   12.121%   $152.0249   $152.02   $152.00   $152.00  
  Purchase #6 $42.83   10.611%   $47.3747   $47.37   $47.35   $47.40  
  Purchase #7 $42.79   7.387%   $45.9509   $45.95   $45.95   $46.00  
  7 purchase totals = $728.35       $799.1319   $799.12   $799.10   $799.10