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 $230.68   11.727%   $257.7318   $257.73   $257.75   $257.70  
  Purchase #2 $183.52   10.529%   $202.8428   $202.84   $202.85   $202.80  
  Purchase #3 $163.89   6.800%   $175.0345   $175.03   $175.05   $175.00  
  Purchase #4 $86.93   11.348%   $96.7948   $96.79   $96.80   $96.80  
  Purchase #5 $25.71   4.560%   $26.8824   $26.88   $26.90   $26.90  
  Purchase #6 $244.97   3.788%   $254.2495   $254.25   $254.25   $254.20  
  Purchase #7 $201.29   13.404%   $228.2709   $228.27   $228.25   $228.30  
  7 purchase totals = $1,136.99       $1,241.8067   $1,241.79   $1,241.85   $1,241.70