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 $82.33   12.449%   $92.5793   $92.58   $92.60   $92.60  
  Purchase #2 $232.29   11.827%   $259.7629   $259.76   $259.75   $259.80  
  Purchase #3 $219.53   5.773%   $232.2035   $232.20   $232.20   $232.20  
  Purchase #4 $196.40   5.339%   $206.8858   $206.89   $206.90   $206.90  
  Purchase #5 $59.56   4.609%   $62.3051   $62.31   $62.30   $62.30  
  Purchase #6 $142.68   12.481%   $160.4879   $160.49   $160.50   $160.50  
  Purchase #7 $216.79   3.546%   $224.4774   $224.48   $224.50   $224.50  
  7 purchase totals = $1,149.58       $1,238.7019   $1,238.71   $1,238.75   $1,238.80