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 $234.98   12.608%   $264.6063   $264.61   $264.60   $264.60  
  Purchase #2 $80.91   13.643%   $91.9486   $91.95   $91.95   $91.90  
  Purchase #3 $74.73   8.220%   $80.8728   $80.87   $80.85   $80.90  
  Purchase #4 $73.55   7.689%   $79.2053   $79.21   $79.20   $79.20  
  Purchase #5 $131.29   3.391%   $135.742   $135.74   $135.75   $135.70  
  Purchase #6 $146.80   5.494%   $154.8652   $154.87   $154.85   $154.90  
  Purchase #7 $202.78   12.107%   $227.3306   $227.33   $227.35   $227.30  
  7 purchase totals = $945.04       $1,034.5708   $1,034.58   $1,034.55   $1,034.50