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 $59.43   10.231%   $65.5103   $65.51   $65.50   $65.50  
  Purchase #2 $242.96   8.827%   $264.4061   $264.41   $264.40   $264.40  
  Purchase #3 $60.73   13.754%   $69.0828   $69.08   $69.10   $69.10  
  Purchase #4 $226.90   8.426%   $246.0186   $246.02   $246.00   $246.00  
  Purchase #5 $87.79   3.802%   $91.1278   $91.13   $91.15   $91.10  
  Purchase #6 $95.32   10.186%   $105.0293   $105.03   $105.05   $105.00  
  Purchase #7 $101.80   7.267%   $109.1978   $109.20   $109.20   $109.20  
  7 purchase totals = $874.93       $950.3727   $950.38   $950.40   $950.30