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 $195.92   11.437%   $218.3274   $218.33   $218.35   $218.30  
  Purchase #2 $87.32   5.163%   $91.8283   $91.83   $91.85   $91.80  
  Purchase #3 $129.33   8.646%   $140.5119   $140.51   $140.50   $140.50  
  Purchase #4 $119.35   4.493%   $124.7124   $124.71   $124.70   $124.70  
  Purchase #5 $109.82   7.477%   $118.0312   $118.03   $118.05   $118.00  
  Purchase #6 $234.40   3.760%   $243.2134   $243.21   $243.20   $243.20  
  Purchase #7 $182.27   4.132%   $189.8014   $189.80   $189.80   $189.80  
  7 purchase totals = $1,058.41       $1,126.4260   $1,126.42   $1,126.45   $1,126.30