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 $91.34   13.334%   $103.5193   $103.52   $103.50   $103.50  
  Purchase #2 $52.39   9.505%   $57.3697   $57.37   $57.35   $57.40  
  Purchase #3 $150.57   6.550%   $160.4323   $160.43   $160.45   $160.40  
  Purchase #4 $160.65   4.287%   $167.5371   $167.54   $167.55   $167.50  
  Purchase #5 $8.55   4.461%   $8.9314   $8.93   $8.95   $8.90  
  Purchase #6 $58.66   3.136%   $60.4996   $60.50   $60.50   $60.50  
  Purchase #7 $177.99   13.443%   $201.9172   $201.92   $201.90   $201.90  
  7 purchase totals = $700.15       $760.2066   $760.21   $760.20   $760.10