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 $239.54   11.233%   $266.4475   $266.45   $266.45   $266.40  
  Purchase #2 $234.57   12.554%   $264.0179   $264.02   $264.00   $264.00  
  Purchase #3 $95.60   4.530%   $99.9307   $99.93   $99.95   $99.90  
  Purchase #4 $235.32   8.264%   $254.7668   $254.77   $254.75   $254.80  
  Purchase #5 $60.87   6.593%   $64.8832   $64.88   $64.90   $64.90  
  Purchase #6 $60.65   12.835%   $68.4344   $68.43   $68.45   $68.40  
  Purchase #7 $211.54   5.566%   $223.3143   $223.31   $223.30   $223.30  
  7 purchase totals = $1,138.09       $1,241.7948   $1,241.79   $1,241.80   $1,241.70