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 $47.59   13.534%   $54.0308   $54.03   $54.05   $54.00  
  Purchase #2 $139.31   11.518%   $155.3557   $155.36   $155.35   $155.40  
  Purchase #3 $231.33   9.490%   $253.2832   $253.28   $253.30   $253.30  
  Purchase #4 $98.32   8.592%   $106.7677   $106.77   $106.75   $106.80  
  Purchase #5 $44.93   7.525%   $48.311   $48.31   $48.30   $48.30  
  Purchase #6 $131.94   4.619%   $138.0343   $138.03   $138.05   $138.00  
  Purchase #7 $180.67   13.313%   $204.7226   $204.72   $204.70   $204.70  
  7 purchase totals = $874.09       $960.5053   $960.50   $960.50   $960.50