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 $241.93   9.423%   $264.7271   $264.73   $264.75   $264.70  
  Purchase #2 $106.35   4.229%   $110.8475   $110.85   $110.85   $110.80  
  Purchase #3 $221.58   10.655%   $245.1893   $245.19   $245.20   $245.20  
  Purchase #4 $165.47   4.234%   $172.476   $172.48   $172.50   $172.50  
  Purchase #5 $65.44   12.203%   $73.4256   $73.43   $73.45   $73.40  
  Purchase #6 $77.43   12.619%   $87.2009   $87.20   $87.20   $87.20  
  Purchase #7 $90.85   9.414%   $99.4026   $99.40   $99.40   $99.40  
  7 purchase totals = $969.05       $1,053.2690   $1,053.28   $1,053.35   $1,053.20