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 $100.45   7.589%   $108.0732   $108.07   $108.05   $108.10  
  Purchase #2 $43.83   9.530%   $48.007   $48.01   $48.00   $48.00  
  Purchase #3 $217.29   4.285%   $226.6009   $226.60   $226.60   $226.60  
  Purchase #4 $44.25   13.840%   $50.3742   $50.37   $50.35   $50.40  
  Purchase #5 $195.52   13.759%   $222.4216   $222.42   $222.40   $222.40  
  Purchase #6 $99.51   7.859%   $107.3305   $107.33   $107.35   $107.30  
  Purchase #7 $105.37   9.220%   $115.0851   $115.09   $115.10   $115.10  
  7 purchase totals = $806.22       $877.8925   $877.89   $877.85   $877.90