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 $218.94   11.401%   $243.9013   $243.90   $243.90   $243.90  
  Purchase #2 $33.98   7.760%   $36.6168   $36.62   $36.60   $36.60  
  Purchase #3 $152.92   10.696%   $169.2763   $169.28   $169.30   $169.30  
  Purchase #4 $112.33   6.707%   $119.864   $119.86   $119.85   $119.90  
  Purchase #5 $218.39   6.253%   $232.0459   $232.05   $232.05   $232.00  
  Purchase #6 $88.99   10.465%   $98.3028   $98.30   $98.30   $98.30  
  Purchase #7 $191.99   5.112%   $201.8045   $201.80   $201.80   $201.80  
  7 purchase totals = $1,017.54       $1,101.8116   $1,101.81   $1,101.80   $1,101.80