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 $52.98   9.621%   $58.0772   $58.08   $58.10   $58.10  
  Purchase #2 $237.65   12.241%   $266.7407   $266.74   $266.75   $266.70  
  Purchase #3 $99.56   10.494%   $110.0078   $110.01   $110.00   $110.00  
  Purchase #4 $164.45   12.531%   $185.0572   $185.06   $185.05   $185.10  
  Purchase #5 $182.40   6.834%   $194.8652   $194.87   $194.85   $194.90  
  Purchase #6 $238.80   10.235%   $263.2412   $263.24   $263.25   $263.20  
  Purchase #7 $106.80   11.733%   $119.3308   $119.33   $119.35   $119.30  
  7 purchase totals = $1,082.64       $1,197.3201   $1,197.33   $1,197.35   $1,197.30