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 $24.68   3.410%   $25.5216   $25.52   $25.50   $25.50  
  Purchase #2 $212.33   6.128%   $225.3416   $225.34   $225.35   $225.30  
  Purchase #3 $29.97   8.252%   $32.4431   $32.44   $32.45   $32.40  
  Purchase #4 $163.94   6.425%   $174.4731   $174.47   $174.45   $174.50  
  Purchase #5 $97.53   7.453%   $104.7989   $104.80   $104.80   $104.80  
  Purchase #6 $114.61   3.331%   $118.4277   $118.43   $118.45   $118.40  
  Purchase #7 $63.85   3.338%   $65.9813   $65.98   $66.00   $66.00  
  7 purchase totals = $706.91       $746.9873   $746.98   $747.00   $746.90