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 $245.74   9.768%   $269.7439   $269.74   $269.75   $269.70  
  Purchase #2 $124.35   13.453%   $141.0788   $141.08   $141.10   $141.10  
  Purchase #3 $72.63   10.415%   $80.1944   $80.19   $80.20   $80.20  
  Purchase #4 $53.31   7.468%   $57.2912   $57.29   $57.30   $57.30  
  Purchase #5 $70.75   5.760%   $74.8252   $74.83   $74.85   $74.80  
  Purchase #6 $191.32   12.417%   $215.0762   $215.08   $215.10   $215.10  
  Purchase #7 $167.54   11.476%   $186.7669   $186.77   $186.75   $186.80  
  7 purchase totals = $925.64       $1,024.9766   $1,024.98   $1,025.05   $1,025.00