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 $79.87   6.771%   $85.278   $85.28   $85.30   $85.30  
  Purchase #2 $217.86   5.830%   $230.5612   $230.56   $230.55   $230.60  
  Purchase #3 $31.29   10.465%   $34.5645   $34.56   $34.55   $34.60  
  Purchase #4 $22.37   10.814%   $24.7891   $24.79   $24.80   $24.80  
  Purchase #5 $150.92   12.731%   $170.1336   $170.13   $170.15   $170.10  
  Purchase #6 $223.83   4.422%   $233.7278   $233.73   $233.75   $233.70  
  Purchase #7 $170.97   7.240%   $183.3482   $183.35   $183.35   $183.30  
  7 purchase totals = $897.11       $962.4024   $962.40   $962.45   $962.40