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 $55.39   10.461%   $61.1843   $61.18   $61.20   $61.20  
  Purchase #2 $223.61   6.117%   $237.2882   $237.29   $237.30   $237.30  
  Purchase #3 $55.28   6.253%   $58.7367   $58.74   $58.75   $58.70  
  Purchase #4 $202.99   7.871%   $218.9673   $218.97   $218.95   $219.00  
  Purchase #5 $99.86   9.831%   $109.6772   $109.68   $109.70   $109.70  
  Purchase #6 $98.94   7.288%   $106.1507   $106.15   $106.15   $106.20  
  Purchase #7 $185.69   13.162%   $210.1305   $210.13   $210.15   $210.10  
  7 purchase totals = $921.76       $1,002.1349   $1,002.14   $1,002.20   $1,002.20