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 $141.94   13.874%   $161.6328   $161.63   $161.65   $161.60  
  Purchase #2 $247.40   3.548%   $256.1778   $256.18   $256.20   $256.20  
  Purchase #3 $188.43   9.299%   $205.9521   $205.95   $205.95   $206.00  
  Purchase #4 $244.74   13.580%   $277.9757   $277.98   $278.00   $278.00  
  Purchase #5 $53.63   5.817%   $56.7497   $56.75   $56.75   $56.70  
  Purchase #6 $129.90   11.154%   $144.389   $144.39   $144.40   $144.40  
  Purchase #7 $23.52   8.148%   $25.4364   $25.44   $25.45   $25.40  
  7 purchase totals = $1,029.56       $1,128.3135   $1,128.32   $1,128.40   $1,128.30