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 $61.95   3.616%   $64.1901   $64.19   $64.20   $64.20  
  Purchase #2 $103.86   11.741%   $116.0542   $116.05   $116.05   $116.10  
  Purchase #3 $200.45   8.867%   $218.2239   $218.22   $218.20   $218.20  
  Purchase #4 $198.39   5.692%   $209.6824   $209.68   $209.70   $209.70  
  Purchase #5 $91.60   12.441%   $102.996   $103.00   $103.00   $103.00  
  Purchase #6 $105.91   13.558%   $120.2693   $120.27   $120.25   $120.30  
  Purchase #7 $198.77   5.548%   $209.7978   $209.80   $209.80   $209.80  
  7 purchase totals = $960.93       $1,041.2137   $1,041.21   $1,041.20   $1,041.30