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 $199.35   13.404%   $226.0709   $226.07   $226.05   $226.10  
  Purchase #2 $54.82   6.403%   $58.3301   $58.33   $58.35   $58.30  
  Purchase #3 $215.32   12.297%   $241.7979   $241.80   $241.80   $241.80  
  Purchase #4 $52.66   7.709%   $56.7196   $56.72   $56.70   $56.70  
  Purchase #5 $118.39   12.342%   $133.0017   $133.00   $133.00   $133.00  
  Purchase #6 $122.51   3.535%   $126.8407   $126.84   $126.85   $126.80  
  Purchase #7 $95.65   6.665%   $102.0251   $102.03   $102.05   $102.00  
  7 purchase totals = $858.70       $944.7860   $944.79   $944.80   $944.70