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 $90.48   11.773%   $101.1322   $101.13   $101.15   $101.10  
  Purchase #2 $66.43   3.301%   $68.6229   $68.62   $68.60   $68.60  
  Purchase #3 $208.32   13.657%   $236.7703   $236.77   $236.75   $236.80  
  Purchase #4 $194.87   7.518%   $209.5203   $209.52   $209.50   $209.50  
  Purchase #5 $175.94   10.606%   $194.6002   $194.60   $194.60   $194.60  
  Purchase #6 $148.82   12.716%   $167.744   $167.74   $167.75   $167.70  
  Purchase #7 $147.38   3.686%   $152.8124   $152.81   $152.80   $152.80  
  7 purchase totals = $1,032.24       $1,131.2023   $1,131.19   $1,131.15   $1,131.10