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 $44.37   6.631%   $47.3122   $47.31   $47.30   $47.30  
  Purchase #2 $203.74   11.555%   $227.2822   $227.28   $227.30   $227.30  
  Purchase #3 $132.94   8.872%   $144.7344   $144.73   $144.75   $144.70  
  Purchase #4 $165.97   11.143%   $184.464   $184.46   $184.45   $184.50  
  Purchase #5 $118.35   11.131%   $131.5235   $131.52   $131.50   $131.50  
  Purchase #6 $34.72   12.472%   $39.0503   $39.05   $39.05   $39.10  
  Purchase #7 $246.39   6.415%   $262.1959   $262.20   $262.20   $262.20  
  7 purchase totals = $946.48       $1,036.5625   $1,036.55   $1,036.55   $1,036.60