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 $93.71   3.221%   $96.7284   $96.73   $96.75   $96.70  
  Purchase #2 $74.36   12.613%   $83.739   $83.74   $83.75   $83.70  
  Purchase #3 $193.68   13.852%   $220.5086   $220.51   $220.50   $220.50  
  Purchase #4 $109.82   13.759%   $124.9301   $124.93   $124.95   $124.90  
  Purchase #5 $209.33   11.122%   $232.6117   $232.61   $232.60   $232.60  
  Purchase #6 $173.98   9.611%   $190.7012   $190.70   $190.70   $190.70  
  Purchase #7 $141.74   13.178%   $160.4185   $160.42   $160.40   $160.40  
  7 purchase totals = $996.62       $1,109.6375   $1,109.64   $1,109.65   $1,109.50