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 $131.27   11.831%   $146.8006   $146.80   $146.80   $146.80  
  Purchase #2 $173.50   13.867%   $197.5592   $197.56   $197.55   $197.60  
  Purchase #3 $82.52   10.247%   $90.9758   $90.98   $91.00   $91.00  
  Purchase #4 $100.72   5.549%   $106.309   $106.31   $106.30   $106.30  
  Purchase #5 $31.35   3.421%   $32.4225   $32.42   $32.40   $32.40  
  Purchase #6 $154.69   5.472%   $163.1546   $163.15   $163.15   $163.20  
  Purchase #7 $171.41   10.182%   $188.863   $188.86   $188.85   $188.90  
  7 purchase totals = $845.46       $926.0847   $926.08   $926.05   $926.20