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 $32.70   12.103%   $36.6577   $36.66   $36.65   $36.70  
  Purchase #2 $110.25   6.453%   $117.3644   $117.36   $117.35   $117.40  
  Purchase #3 $151.55   13.711%   $172.329   $172.33   $172.35   $172.30  
  Purchase #4 $46.94   7.156%   $50.299   $50.30   $50.30   $50.30  
  Purchase #5 $200.39   6.586%   $213.5877   $213.59   $213.60   $213.60  
  Purchase #6 $8.28   7.810%   $8.9267   $8.93   $8.95   $8.90  
  Purchase #7 $91.27   5.799%   $96.5627   $96.56   $96.55   $96.60  
  7 purchase totals = $641.38       $695.7272   $695.73   $695.75   $695.80