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 $89.82   6.105%   $95.3035   $95.30   $95.30   $95.30  
  Purchase #2 $157.52   8.325%   $170.6335   $170.63   $170.65   $170.60  
  Purchase #3 $151.97   11.244%   $169.0575   $169.06   $169.05   $169.10  
  Purchase #4 $192.39   3.777%   $199.6566   $199.66   $199.65   $199.70  
  Purchase #5 $178.30   3.534%   $184.6011   $184.60   $184.60   $184.60  
  Purchase #6 $236.32   12.125%   $264.9738   $264.97   $264.95   $265.00  
  Purchase #7 $55.79   12.744%   $62.8999   $62.90   $62.90   $62.90  
  7 purchase totals = $1,062.11       $1,147.1259   $1,147.12   $1,147.10   $1,147.20