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 $238.72   9.257%   $260.8183   $260.82   $260.80   $260.80  
  Purchase #2 $211.38   4.802%   $221.5305   $221.53   $221.55   $221.50  
  Purchase #3 $195.27   7.121%   $209.1752   $209.18   $209.20   $209.20  
  Purchase #4 $84.53   9.434%   $92.5046   $92.50   $92.50   $92.50  
  Purchase #5 $98.31   9.367%   $107.5187   $107.52   $107.50   $107.50  
  Purchase #6 $63.66   7.277%   $68.2925   $68.29   $68.30   $68.30  
  Purchase #7 $38.77   7.229%   $41.5727   $41.57   $41.55   $41.60  
  7 purchase totals = $930.64       $1,001.4125   $1,001.41   $1,001.40   $1,001.40