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 $242.56   13.790%   $276.009   $276.01   $276.00   $276.00  
  Purchase #2 $24.92   9.777%   $27.3564   $27.36   $27.35   $27.40  
  Purchase #3 $137.71   11.481%   $153.5205   $153.52   $153.50   $153.50  
  Purchase #4 $44.33   12.367%   $49.8123   $49.81   $49.80   $49.80  
  Purchase #5 $54.95   3.657%   $56.9595   $56.96   $56.95   $57.00  
  Purchase #6 $69.86   7.517%   $75.1114   $75.11   $75.10   $75.10  
  Purchase #7 $212.29   10.518%   $234.6187   $234.62   $234.60   $234.60  
  7 purchase totals = $786.62       $873.3878   $873.39   $873.30   $873.40