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 $218.80   9.114%   $238.7414   $238.74   $238.75   $238.70  
  Purchase #2 $33.45   7.537%   $35.9711   $35.97   $35.95   $36.00  
  Purchase #3 $134.94   13.369%   $152.9801   $152.98   $153.00   $153.00  
  Purchase #4 $204.71   8.213%   $221.5228   $221.52   $221.50   $221.50  
  Purchase #5 $42.61   9.401%   $46.6158   $46.62   $46.60   $46.60  
  Purchase #6 $178.52   5.834%   $188.9349   $188.93   $188.95   $188.90  
  Purchase #7 $149.37   12.190%   $167.5782   $167.58   $167.60   $167.60  
  7 purchase totals = $962.40       $1,052.3443   $1,052.34   $1,052.35   $1,052.30