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 $91.82   5.225%   $96.6176   $96.62   $96.60   $96.60  
  Purchase #2 $27.52   13.351%   $31.1942   $31.19   $31.20   $31.20  
  Purchase #3 $139.49   3.473%   $144.3345   $144.33   $144.35   $144.30  
  Purchase #4 $241.68   6.310%   $256.93   $256.93   $256.95   $256.90  
  Purchase #5 $193.69   5.115%   $203.5972   $203.60   $203.60   $203.60  
  Purchase #6 $168.29   9.444%   $184.1833   $184.18   $184.20   $184.20  
  Purchase #7 $43.94   9.683%   $48.1947   $48.19   $48.20   $48.20  
  7 purchase totals = $906.43       $965.0515   $965.04   $965.10   $965.00