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 $125.50   3.831%   $130.3079   $130.31   $130.30   $130.30  
  Purchase #2 $183.51   6.615%   $195.6492   $195.65   $195.65   $195.60  
  Purchase #3 $43.92   5.566%   $46.3646   $46.36   $46.35   $46.40  
  Purchase #4 $146.82   13.791%   $167.0679   $167.07   $167.05   $167.10  
  Purchase #5 $211.45   3.540%   $218.9353   $218.94   $218.95   $218.90  
  Purchase #6 $85.45   7.418%   $91.7887   $91.79   $91.80   $91.80  
  Purchase #7 $202.87   6.525%   $216.1073   $216.11   $216.10   $216.10  
  7 purchase totals = $999.52       $1,066.2209   $1,066.23   $1,066.20   $1,066.20