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 $91.71   5.552%   $96.8017   $96.80   $96.80   $96.80  
  Purchase #2 $53.50   11.752%   $59.7873   $59.79   $59.80   $59.80  
  Purchase #3 $114.44   3.264%   $118.1753   $118.18   $118.20   $118.20  
  Purchase #4 $185.84   6.257%   $197.468   $197.47   $197.45   $197.50  
  Purchase #5 $87.46   9.720%   $95.9611   $95.96   $95.95   $96.00  
  Purchase #6 $28.55   3.695%   $29.6049   $29.60   $29.60   $29.60  
  Purchase #7 $54.62   3.850%   $56.7229   $56.72   $56.70   $56.70  
  7 purchase totals = $616.12       $654.5212   $654.52   $654.50   $654.60