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 $91.59   3.748%   $95.0228   $95.02   $95.00   $95.00  
  Purchase #2 $37.88   8.305%   $41.0259   $41.03   $41.05   $41.00  
  Purchase #3 $84.67   6.495%   $90.1693   $90.17   $90.15   $90.20  
  Purchase #4 $216.36   3.478%   $223.885   $223.89   $223.90   $223.90  
  Purchase #5 $237.82   8.283%   $257.5186   $257.52   $257.50   $257.50  
  Purchase #6 $232.75   3.463%   $240.8101   $240.81   $240.80   $240.80  
  Purchase #7 $123.55   7.619%   $132.9633   $132.96   $132.95   $133.00  
  7 purchase totals = $1,024.62       $1,081.3950   $1,081.40   $1,081.35   $1,081.40