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 $199.82   9.457%   $218.717   $218.72   $218.70   $218.70  
  Purchase #2 $113.90   4.764%   $119.3262   $119.33   $119.35   $119.30  
  Purchase #3 $60.63   3.370%   $62.6732   $62.67   $62.65   $62.70  
  Purchase #4 $217.92   8.535%   $236.5195   $236.52   $236.50   $236.50  
  Purchase #5 $202.77   12.539%   $228.1953   $228.20   $228.20   $228.20  
  Purchase #6 $169.67   10.733%   $187.8807   $187.88   $187.90   $187.90  
  Purchase #7 $225.32   9.195%   $246.0382   $246.04   $246.05   $246.00  
  7 purchase totals = $1,190.03       $1,299.3501   $1,299.36   $1,299.35   $1,299.30