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 $122.65   9.667%   $134.5066   $134.51   $134.50   $134.50  
  Purchase #2 $114.89   5.481%   $121.1871   $121.19   $121.20   $121.20  
  Purchase #3 $244.31   5.372%   $257.4343   $257.43   $257.45   $257.40  
  Purchase #4 $154.57   9.636%   $169.4644   $169.46   $169.45   $169.50  
  Purchase #5 $250.94   5.122%   $263.7931   $263.79   $263.80   $263.80  
  Purchase #6 $5.65   11.393%   $6.2937   $6.29   $6.30   $6.30  
  Purchase #7 $193.46   10.814%   $214.3808   $214.38   $214.40   $214.40  
  7 purchase totals = $1,086.47       $1,167.0600   $1,167.05   $1,167.10   $1,167.10