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 $157.79   12.143%   $176.9504   $176.95   $176.95   $177.00  
  Purchase #2 $22.58   13.817%   $25.6999   $25.70   $25.70   $25.70  
  Purchase #3 $161.79   13.852%   $184.2012   $184.20   $184.20   $184.20  
  Purchase #4 $229.52   8.751%   $249.6053   $249.61   $249.60   $249.60  
  Purchase #5 $93.26   9.824%   $102.4219   $102.42   $102.40   $102.40  
  Purchase #6 $211.90   4.350%   $221.1177   $221.12   $221.10   $221.10  
  Purchase #7 $144.93   10.296%   $159.852   $159.85   $159.85   $159.90  
  7 purchase totals = $1,021.77       $1,119.8484   $1,119.85   $1,119.80   $1,119.90