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 $70.57   4.384%   $73.6638   $73.66   $73.65   $73.70  
  Purchase #2 $183.57   7.828%   $197.9399   $197.94   $197.95   $197.90  
  Purchase #3 $120.55   10.805%   $133.5754   $133.58   $133.60   $133.60  
  Purchase #4 $97.38   9.429%   $106.562   $106.56   $106.55   $106.60  
  Purchase #5 $182.50   8.797%   $198.5545   $198.55   $198.55   $198.60  
  Purchase #6 $239.33   8.684%   $260.1134   $260.11   $260.10   $260.10  
  Purchase #7 $181.35   8.283%   $196.3712   $196.37   $196.35   $196.40  
  7 purchase totals = $1,075.25       $1,166.7802   $1,166.77   $1,166.75   $1,166.90