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 $56.43   6.606%   $60.1578   $60.16   $60.15   $60.20  
  Purchase #2 $175.32   11.652%   $195.7483   $195.75   $195.75   $195.70  
  Purchase #3 $160.57   12.165%   $180.1033   $180.10   $180.10   $180.10  
  Purchase #4 $93.25   13.767%   $106.0877   $106.09   $106.10   $106.10  
  Purchase #5 $241.38   3.791%   $250.5307   $250.53   $250.55   $250.50  
  Purchase #6 $160.52   9.499%   $175.7678   $175.77   $175.75   $175.80  
  Purchase #7 $153.91   9.240%   $168.1313   $168.13   $168.15   $168.10  
  7 purchase totals = $1,041.38       $1,136.5269   $1,136.53   $1,136.55   $1,136.50