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 $244.63   8.822%   $266.2113   $266.21   $266.20   $266.20  
  Purchase #2 $55.98   5.653%   $59.1445   $59.14   $59.15   $59.10  
  Purchase #3 $148.98   13.569%   $169.1951   $169.20   $169.20   $169.20  
  Purchase #4 $102.84   13.296%   $116.5136   $116.51   $116.50   $116.50  
  Purchase #5 $24.94   9.571%   $27.327   $27.33   $27.35   $27.30  
  Purchase #6 $48.66   7.148%   $52.1382   $52.14   $52.15   $52.10  
  Purchase #7 $212.80   6.142%   $225.8702   $225.87   $225.85   $225.90  
  7 purchase totals = $838.83       $916.3999   $916.40   $916.40   $916.30