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 $106.56   11.278%   $118.5778   $118.58   $118.60   $118.60  
  Purchase #2 $239.57   13.575%   $272.0916   $272.09   $272.10   $272.10  
  Purchase #3 $172.85   7.753%   $186.2511   $186.25   $186.25   $186.30  
  Purchase #4 $87.49   6.845%   $93.4787   $93.48   $93.50   $93.50  
  Purchase #5 $172.90   9.504%   $189.3324   $189.33   $189.35   $189.30  
  Purchase #6 $124.64   4.157%   $129.8213   $129.82   $129.80   $129.80  
  Purchase #7 $159.35   5.120%   $167.5087   $167.51   $167.50   $167.50  
  7 purchase totals = $1,063.36       $1,157.0616   $1,157.06   $1,157.10   $1,157.10