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 $232.58   7.580%   $250.2096   $250.21   $250.20   $250.20  
  Purchase #2 $91.51   5.648%   $96.6785   $96.68   $96.70   $96.70  
  Purchase #3 $10.25   9.574%   $11.2313   $11.23   $11.25   $11.20  
  Purchase #4 $217.69   5.730%   $230.1636   $230.16   $230.15   $230.20  
  Purchase #5 $246.29   4.471%   $257.3016   $257.30   $257.30   $257.30  
  Purchase #6 $29.52   4.596%   $30.8767   $30.88   $30.90   $30.90  
  Purchase #7 $147.37   8.691%   $160.1779   $160.18   $160.20   $160.20  
  7 purchase totals = $975.21       $1,036.6392   $1,036.64   $1,036.70   $1,036.70