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 $126.82   10.822%   $140.5445   $140.54   $140.55   $140.50  
  Purchase #2 $88.98   4.832%   $93.2795   $93.28   $93.30   $93.30  
  Purchase #3 $220.80   5.737%   $233.4673   $233.47   $233.45   $233.50  
  Purchase #4 $64.97   7.240%   $69.6738   $69.67   $69.65   $69.70  
  Purchase #5 $186.35   9.565%   $204.1744   $204.17   $204.15   $204.20  
  Purchase #6 $99.87   10.473%   $110.3294   $110.33   $110.35   $110.30  
  Purchase #7 $153.29   5.750%   $162.1042   $162.10   $162.10   $162.10  
  7 purchase totals = $941.08       $1,013.5731   $1,013.56   $1,013.55   $1,013.60