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 $248.92   7.120%   $266.6431   $266.64   $266.65   $266.60  
  Purchase #2 $216.71   11.226%   $241.0379   $241.04   $241.05   $241.00  
  Purchase #3 $78.33   11.666%   $87.468   $87.47   $87.45   $87.50  
  Purchase #4 $126.60   9.744%   $138.9359   $138.94   $138.95   $138.90  
  Purchase #5 $101.82   4.217%   $106.1137   $106.11   $106.10   $106.10  
  Purchase #6 $209.85   10.599%   $232.092   $232.09   $232.10   $232.10  
  Purchase #7 $121.94   6.762%   $130.1856   $130.19   $130.20   $130.20  
  7 purchase totals = $1,104.17       $1,202.4762   $1,202.48   $1,202.50   $1,202.40