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 $88.52   6.209%   $94.0162   $94.02   $94.00   $94.00  
  Purchase #2 $142.65   11.468%   $159.0091   $159.01   $159.00   $159.00  
  Purchase #3 $47.49   11.362%   $52.8858   $52.89   $52.90   $52.90  
  Purchase #4 $171.65   13.312%   $194.5   $194.50   $194.50   $194.50  
  Purchase #5 $39.86   12.496%   $44.8409   $44.84   $44.85   $44.80  
  Purchase #6 $233.56   3.371%   $241.4333   $241.43   $241.45   $241.40  
  Purchase #7 $250.29   12.439%   $281.4236   $281.42   $281.40   $281.40  
  7 purchase totals = $974.02       $1,068.1089   $1,068.11   $1,068.10   $1,068.00