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 $81.41   12.567%   $91.6408   $91.64   $91.65   $91.60  
  Purchase #2 $97.57   13.405%   $110.6493   $110.65   $110.65   $110.60  
  Purchase #3 $229.74   11.159%   $255.3767   $255.38   $255.40   $255.40  
  Purchase #4 $83.93   13.149%   $94.966   $94.97   $94.95   $95.00  
  Purchase #5 $221.81   5.624%   $234.2846   $234.28   $234.30   $234.30  
  Purchase #6 $240.67   13.236%   $272.5251   $272.53   $272.55   $272.50  
  Purchase #7 $21.79   10.147%   $24.001   $24.00   $24.00   $24.00  
  7 purchase totals = $976.92       $1,083.4435   $1,083.45   $1,083.50   $1,083.40