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 $164.51   10.547%   $181.8609   $181.86   $181.85   $181.90  
  Purchase #2 $183.80   6.277%   $195.3371   $195.34   $195.35   $195.30  
  Purchase #3 $32.77   10.700%   $36.2764   $36.28   $36.30   $36.30  
  Purchase #4 $104.53   13.820%   $118.976   $118.98   $119.00   $119.00  
  Purchase #5 $232.33   13.114%   $262.7978   $262.80   $262.80   $262.80  
  Purchase #6 $232.98   7.216%   $249.7918   $249.79   $249.80   $249.80  
  Purchase #7 $20.46   13.761%   $23.2755   $23.28   $23.30   $23.30  
  7 purchase totals = $971.38       $1,068.3155   $1,068.33   $1,068.40   $1,068.40