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 $198.86   12.433%   $223.5843   $223.58   $223.60   $223.60  
  Purchase #2 $201.64   5.123%   $211.97   $211.97   $211.95   $212.00  
  Purchase #3 $98.27   6.746%   $104.8993   $104.90   $104.90   $104.90  
  Purchase #4 $68.46   13.465%   $77.6781   $77.68   $77.70   $77.70  
  Purchase #5 $165.89   3.761%   $172.1291   $172.13   $172.15   $172.10  
  Purchase #6 $10.37   7.753%   $11.174   $11.17   $11.15   $11.20  
  Purchase #7 $23.99   11.316%   $26.7047   $26.70   $26.70   $26.70  
  7 purchase totals = $767.48       $828.1395   $828.13   $828.15   $828.20