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 $200.33   3.478%   $207.2975   $207.30   $207.30   $207.30  
  Purchase #2 $54.71   7.771%   $58.9615   $58.96   $58.95   $59.00  
  Purchase #3 $25.93   3.385%   $26.8077   $26.81   $26.80   $26.80  
  Purchase #4 $154.28   9.618%   $169.1187   $169.12   $169.10   $169.10  
  Purchase #5 $242.66   9.560%   $265.8583   $265.86   $265.85   $265.90  
  Purchase #6 $36.64   10.688%   $40.5561   $40.56   $40.55   $40.60  
  Purchase #7 $116.38   3.348%   $120.2764   $120.28   $120.30   $120.30  
  7 purchase totals = $830.93       $888.8762   $888.89   $888.85   $889.00