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 $60.65   9.816%   $66.6034   $66.60   $66.60   $66.60  
  Purchase #2 $243.63   12.405%   $273.8523   $273.85   $273.85   $273.90  
  Purchase #3 $184.92   7.863%   $199.4603   $199.46   $199.45   $199.50  
  Purchase #4 $25.67   8.189%   $27.7721   $27.77   $27.75   $27.80  
  Purchase #5 $203.39   8.156%   $219.9785   $219.98   $220.00   $220.00  
  Purchase #6 $11.62   3.648%   $12.0439   $12.04   $12.05   $12.00  
  Purchase #7 $247.32   11.322%   $275.3216   $275.32   $275.30   $275.30  
  7 purchase totals = $977.20       $1,075.0321   $1,075.02   $1,075.00   $1,075.10