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 $49.91   11.762%   $55.7804   $55.78   $55.80   $55.80  
  Purchase #2 $238.66   10.168%   $262.9269   $262.93   $262.95   $262.90  
  Purchase #3 $205.89   6.429%   $219.1267   $219.13   $219.15   $219.10  
  Purchase #4 $134.75   4.586%   $140.9296   $140.93   $140.95   $140.90  
  Purchase #5 $122.59   10.651%   $135.6471   $135.65   $135.65   $135.60  
  Purchase #6 $95.64   11.530%   $106.6673   $106.67   $106.65   $106.70  
  Purchase #7 $218.62   8.404%   $236.9928   $236.99   $237.00   $237.00  
  7 purchase totals = $1,066.06       $1,158.0708   $1,158.08   $1,158.15   $1,158.00