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 $134.95   4.466%   $140.9769   $140.98   $141.00   $141.00  
  Purchase #2 $61.56   6.813%   $65.7541   $65.75   $65.75   $65.80  
  Purchase #3 $31.80   7.525%   $34.193   $34.19   $34.20   $34.20  
  Purchase #4 $205.77   6.724%   $219.606   $219.61   $219.60   $219.60  
  Purchase #5 $118.70   13.132%   $134.2877   $134.29   $134.30   $134.30  
  Purchase #6 $57.87   11.510%   $64.5308   $64.53   $64.55   $64.50  
  Purchase #7 $175.29   9.779%   $192.4316   $192.43   $192.45   $192.40  
  7 purchase totals = $785.94       $851.7801   $851.78   $851.85   $851.80