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 $169.94   7.593%   $182.8435   $182.84   $182.85   $182.80  
  Purchase #2 $56.66   3.728%   $58.7723   $58.77   $58.75   $58.80  
  Purchase #3 $147.80   9.764%   $162.2312   $162.23   $162.25   $162.20  
  Purchase #4 $226.92   7.343%   $243.5827   $243.58   $243.60   $243.60  
  Purchase #5 $106.96   11.852%   $119.6369   $119.64   $119.65   $119.60  
  Purchase #6 $216.93   10.682%   $240.1025   $240.10   $240.10   $240.10  
  Purchase #7 $144.50   3.714%   $149.8667   $149.87   $149.85   $149.90  
  7 purchase totals = $1,069.71       $1,157.0358   $1,157.03   $1,157.05   $1,157.00