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 $57.84   10.460%   $63.8901   $63.89   $63.90   $63.90  
  Purchase #2 $93.30   10.348%   $102.9547   $102.95   $102.95   $103.00  
  Purchase #3 $133.55   10.165%   $147.1254   $147.13   $147.15   $147.10  
  Purchase #4 $164.32   11.351%   $182.972   $182.97   $182.95   $183.00  
  Purchase #5 $228.51   5.653%   $241.4277   $241.43   $241.45   $241.40  
  Purchase #6 $28.70   8.723%   $31.2035   $31.20   $31.20   $31.20  
  Purchase #7 $24.55   3.179%   $25.3304   $25.33   $25.35   $25.30  
  7 purchase totals = $730.77       $794.9038   $794.90   $794.95   $794.90