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 $64.96   6.813%   $69.3857   $69.39   $69.40   $69.40  
  Purchase #2 $128.66   5.586%   $135.8469   $135.85   $135.85   $135.80  
  Purchase #3 $228.92   13.659%   $260.1882   $260.19   $260.20   $260.20  
  Purchase #4 $54.57   7.573%   $58.7026   $58.70   $58.70   $58.70  
  Purchase #5 $85.42   6.159%   $90.681   $90.68   $90.70   $90.70  
  Purchase #6 $137.94   9.485%   $151.0236   $151.02   $151.00   $151.00  
  Purchase #7 $114.31   4.783%   $119.7774   $119.78   $119.80   $119.80  
  7 purchase totals = $814.78       $885.6054   $885.61   $885.65   $885.60