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 $172.86   12.565%   $194.5799   $194.58   $194.60   $194.60  
  Purchase #2 $69.63   5.315%   $73.3308   $73.33   $73.35   $73.30  
  Purchase #3 $29.74   9.356%   $32.5225   $32.52   $32.50   $32.50  
  Purchase #4 $49.33   8.561%   $53.5531   $53.55   $53.55   $53.60  
  Purchase #5 $207.47   8.450%   $225.0012   $225.00   $225.00   $225.00  
  Purchase #6 $179.92   12.414%   $202.2553   $202.26   $202.25   $202.30  
  Purchase #7 $60.40   3.766%   $62.6747   $62.67   $62.65   $62.70  
  7 purchase totals = $769.35       $843.9175   $843.91   $843.90   $844.00