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 $52.67   13.703%   $59.8874   $59.89   $59.90   $59.90  
  Purchase #2 $186.83   8.218%   $202.1837   $202.18   $202.20   $202.20  
  Purchase #3 $250.96   9.408%   $274.5703   $274.57   $274.55   $274.60  
  Purchase #4 $160.28   4.561%   $167.5904   $167.59   $167.60   $167.60  
  Purchase #5 $14.30   7.355%   $15.3518   $15.35   $15.35   $15.40  
  Purchase #6 $60.46   10.185%   $66.6179   $66.62   $66.60   $66.60  
  Purchase #7 $36.69   5.842%   $38.8334   $38.83   $38.85   $38.80  
  7 purchase totals = $762.19       $825.0349   $825.03   $825.05   $825.10