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 $227.37   11.553%   $253.6381   $253.64   $253.65   $253.60  
  Purchase #2 $202.96   4.573%   $212.2414   $212.24   $212.25   $212.20  
  Purchase #3 $34.95   6.319%   $37.1585   $37.16   $37.15   $37.20  
  Purchase #4 $167.29   10.111%   $184.2047   $184.20   $184.20   $184.20  
  Purchase #5 $74.62   10.662%   $82.576   $82.58   $82.60   $82.60  
  Purchase #6 $29.67   7.652%   $31.9403   $31.94   $31.95   $31.90  
  Purchase #7 $217.87   11.635%   $243.2192   $243.22   $243.20   $243.20  
  7 purchase totals = $954.73       $1,044.9782   $1,044.98   $1,045.00   $1,044.90