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 $89.85   5.308%   $94.6192   $94.62   $94.60   $94.60  
  Purchase #2 $61.37   4.539%   $64.1556   $64.16   $64.15   $64.20  
  Purchase #3 $68.34   11.180%   $75.9804   $75.98   $76.00   $76.00  
  Purchase #4 $227.95   6.291%   $242.2903   $242.29   $242.30   $242.30  
  Purchase #5 $133.98   7.283%   $143.7378   $143.74   $143.75   $143.70  
  Purchase #6 $145.59   4.290%   $151.8358   $151.84   $151.85   $151.80  
  Purchase #7 $170.72   11.123%   $189.7092   $189.71   $189.70   $189.70  
  7 purchase totals = $897.80       $962.3283   $962.34   $962.35   $962.30