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 $36.57   13.159%   $41.3822   $41.38   $41.40   $41.40  
  Purchase #2 $181.84   11.804%   $203.3044   $203.30   $203.30   $203.30  
  Purchase #3 $183.64   10.710%   $203.3078   $203.31   $203.30   $203.30  
  Purchase #4 $23.90   7.108%   $25.5988   $25.60   $25.60   $25.60  
  Purchase #5 $230.70   5.697%   $243.843   $243.84   $243.85   $243.80  
  Purchase #6 $102.38   5.473%   $107.9833   $107.98   $108.00   $108.00  
  Purchase #7 $85.85   6.383%   $91.3298   $91.33   $91.35   $91.30  
  7 purchase totals = $844.88       $916.7493   $916.74   $916.80   $916.70