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 $151.59   6.398%   $161.2887   $161.29   $161.30   $161.30  
  Purchase #2 $62.98   4.773%   $65.986   $65.99   $66.00   $66.00  
  Purchase #3 $106.68   13.852%   $121.4573   $121.46   $121.45   $121.50  
  Purchase #4 $238.49   12.168%   $267.5095   $267.51   $267.50   $267.50  
  Purchase #5 $173.53   7.216%   $186.0519   $186.05   $186.05   $186.10  
  Purchase #6 $196.65   3.774%   $204.0716   $204.07   $204.05   $204.10  
  Purchase #7 $38.80   4.634%   $40.598   $40.60   $40.60   $40.60  
  7 purchase totals = $968.72       $1,046.9630   $1,046.97   $1,046.95   $1,047.10