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 $246.80   9.809%   $271.0086   $271.01   $271.00   $271.00  
  Purchase #2 $231.96   6.348%   $246.6848   $246.68   $246.70   $246.70  
  Purchase #3 $157.57   4.822%   $165.168   $165.17   $165.15   $165.20  
  Purchase #4 $30.43   11.611%   $33.9632   $33.96   $33.95   $34.00  
  Purchase #5 $193.73   10.442%   $213.9593   $213.96   $213.95   $214.00  
  Purchase #6 $144.45   4.843%   $151.4457   $151.45   $151.45   $151.40  
  Purchase #7 $61.79   3.360%   $63.8661   $63.87   $63.85   $63.90  
  7 purchase totals = $1,066.73       $1,146.0957   $1,146.10   $1,146.05   $1,146.20