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 $211.70   13.853%   $241.0268   $241.03   $241.05   $241.00  
  Purchase #2 $147.52   5.137%   $155.0981   $155.10   $155.10   $155.10  
  Purchase #3 $241.84   5.846%   $255.978   $255.98   $256.00   $256.00  
  Purchase #4 $94.43   7.714%   $101.7143   $101.71   $101.70   $101.70  
  Purchase #5 $110.85   4.589%   $115.9369   $115.94   $115.95   $115.90  
  Purchase #6 $226.59   3.274%   $234.0086   $234.01   $234.00   $234.00  
  Purchase #7 $246.87   11.155%   $274.4083   $274.41   $274.40   $274.40  
  7 purchase totals = $1,279.80       $1,378.1710   $1,378.18   $1,378.20   $1,378.10