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 $44.41   8.828%   $48.3305   $48.33   $48.35   $48.30  
  Purchase #2 $97.79   11.544%   $109.0789   $109.08   $109.10   $109.10  
  Purchase #3 $116.47   4.552%   $121.7717   $121.77   $121.75   $121.80  
  Purchase #4 $81.26   8.619%   $88.2638   $88.26   $88.25   $88.30  
  Purchase #5 $93.63   6.847%   $100.0408   $100.04   $100.05   $100.00  
  Purchase #6 $235.28   6.717%   $251.0838   $251.08   $251.10   $251.10  
  Purchase #7 $138.35   12.317%   $155.3906   $155.39   $155.40   $155.40  
  7 purchase totals = $807.19       $873.9601   $873.95   $874.00   $874.00