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 $91.53   5.309%   $96.3893   $96.39   $96.40   $96.40  
  Purchase #2 $185.86   3.290%   $191.9748   $191.97   $191.95   $192.00  
  Purchase #3 $180.60   12.639%   $203.426   $203.43   $203.45   $203.40  
  Purchase #4 $53.73   13.858%   $61.1759   $61.18   $61.20   $61.20  
  Purchase #5 $245.82   12.692%   $277.0195   $277.02   $277.00   $277.00  
  Purchase #6 $71.67   5.121%   $75.3402   $75.34   $75.35   $75.30  
  Purchase #7 $208.97   6.719%   $223.0107   $223.01   $223.00   $223.00  
  7 purchase totals = $1,038.18       $1,128.3364   $1,128.34   $1,128.35   $1,128.30