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 $160.83   9.309%   $175.8017   $175.80   $175.80   $175.80  
  Purchase #2 $184.82   10.193%   $203.6587   $203.66   $203.65   $203.70  
  Purchase #3 $124.81   6.572%   $133.0125   $133.01   $133.00   $133.00  
  Purchase #4 $111.47   6.334%   $118.5305   $118.53   $118.55   $118.50  
  Purchase #5 $221.37   11.787%   $247.4629   $247.46   $247.45   $247.50  
  Purchase #6 $244.63   11.263%   $272.1827   $272.18   $272.20   $272.20  
  Purchase #7 $67.91   11.619%   $75.8005   $75.80   $75.80   $75.80  
  7 purchase totals = $1,115.84       $1,226.4495   $1,226.44   $1,226.45   $1,226.50