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 $84.78   9.836%   $93.119   $93.12   $93.10   $93.10  
  Purchase #2 $181.63   7.397%   $195.0652   $195.07   $195.05   $195.10  
  Purchase #3 $80.96   5.442%   $85.3658   $85.37   $85.35   $85.40  
  Purchase #4 $230.44   5.829%   $243.8723   $243.87   $243.85   $243.90  
  Purchase #5 $249.64   5.200%   $262.6213   $262.62   $262.60   $262.60  
  Purchase #6 $176.57   9.209%   $192.8303   $192.83   $192.85   $192.80  
  Purchase #7 $67.51   3.723%   $70.0234   $70.02   $70.00   $70.00  
  7 purchase totals = $1,071.53       $1,142.8973   $1,142.90   $1,142.80   $1,142.90