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 $218.62   10.410%   $241.3783   $241.38   $241.40   $241.40  
  Purchase #2 $165.74   12.853%   $187.0426   $187.04   $187.05   $187.00  
  Purchase #3 $48.38   13.221%   $54.7763   $54.78   $54.80   $54.80  
  Purchase #4 $176.43   12.391%   $198.2914   $198.29   $198.30   $198.30  
  Purchase #5 $170.66   3.277%   $176.2525   $176.25   $176.25   $176.30  
  Purchase #6 $107.89   5.391%   $113.7063   $113.71   $113.70   $113.70  
  Purchase #7 $169.96   5.710%   $179.6647   $179.66   $179.65   $179.70  
  7 purchase totals = $1,057.68       $1,151.1121   $1,151.11   $1,151.15   $1,151.20