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 $33.95   7.679%   $36.557   $36.56   $36.55   $36.60  
  Purchase #2 $52.67   7.380%   $56.557   $56.56   $56.55   $56.60  
  Purchase #3 $57.82   11.825%   $64.6572   $64.66   $64.65   $64.70  
  Purchase #4 $64.41   7.498%   $69.2395   $69.24   $69.25   $69.20  
  Purchase #5 $169.53   3.522%   $175.5008   $175.50   $175.50   $175.50  
  Purchase #6 $138.79   8.688%   $150.8481   $150.85   $150.85   $150.80  
  Purchase #7 $40.98   9.437%   $44.8473   $44.85   $44.85   $44.80  
  7 purchase totals = $558.15       $598.2069   $598.22   $598.20   $598.20