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 $188.68   3.322%   $194.9479   $194.95   $194.95   $194.90  
  Purchase #2 $26.43   5.851%   $27.9764   $27.98   $28.00   $28.00  
  Purchase #3 $245.40   4.782%   $257.135   $257.14   $257.15   $257.10  
  Purchase #4 $54.70   8.452%   $59.3232   $59.32   $59.30   $59.30  
  Purchase #5 $211.36   3.829%   $219.453   $219.45   $219.45   $219.50  
  Purchase #6 $183.75   11.419%   $204.7324   $204.73   $204.75   $204.70  
  Purchase #7 $10.74   9.732%   $11.7852   $11.79   $11.80   $11.80  
  7 purchase totals = $921.06       $975.3531   $975.36   $975.40   $975.30