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 $64.71   7.475%   $69.5471   $69.55   $69.55   $69.50  
  Purchase #2 $232.80   6.214%   $247.2662   $247.27   $247.25   $247.30  
  Purchase #3 $121.52   5.558%   $128.2741   $128.27   $128.25   $128.30  
  Purchase #4 $102.34   7.516%   $110.0319   $110.03   $110.05   $110.00  
  Purchase #5 $202.92   10.224%   $223.6665   $223.67   $223.65   $223.70  
  Purchase #6 $13.92   10.722%   $15.4125   $15.41   $15.40   $15.40  
  Purchase #7 $184.47   5.242%   $194.1399   $194.14   $194.15   $194.10  
  7 purchase totals = $922.68       $988.3382   $988.34   $988.30   $988.30