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 $33.69   9.421%   $36.8639   $36.86   $36.85   $36.90  
  Purchase #2 $207.40   7.555%   $223.0691   $223.07   $223.05   $223.10  
  Purchase #3 $192.35   4.150%   $200.3325   $200.33   $200.35   $200.30  
  Purchase #4 $133.82   11.424%   $149.1076   $149.11   $149.10   $149.10  
  Purchase #5 $240.69   11.549%   $268.4873   $268.49   $268.50   $268.50  
  Purchase #6 $146.81   5.783%   $155.3   $155.30   $155.30   $155.30  
  Purchase #7 $26.98   9.346%   $29.5016   $29.50   $29.50   $29.50  
  7 purchase totals = $981.74       $1,062.6620   $1,062.66   $1,062.65   $1,062.70