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 $146.99   10.198%   $161.98   $161.98   $162.00   $162.00  
  Purchase #2 $124.98   3.436%   $129.2743   $129.27   $129.25   $129.30  
  Purchase #3 $12.32   10.435%   $13.6056   $13.61   $13.60   $13.60  
  Purchase #4 $209.68   3.835%   $217.7212   $217.72   $217.70   $217.70  
  Purchase #5 $87.65   6.149%   $93.0396   $93.04   $93.05   $93.00  
  Purchase #6 $149.35   12.673%   $168.2771   $168.28   $168.30   $168.30  
  Purchase #7 $247.56   7.844%   $266.9786   $266.98   $267.00   $267.00  
  7 purchase totals = $978.53       $1,050.8764   $1,050.88   $1,050.90   $1,050.90