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 $6.52   11.355%   $7.2603   $7.26   $7.25   $7.30  
  Purchase #2 $139.98   9.297%   $152.9939   $152.99   $153.00   $153.00  
  Purchase #3 $162.75   3.134%   $167.8506   $167.85   $167.85   $167.90  
  Purchase #4 $192.33   11.418%   $214.2902   $214.29   $214.30   $214.30  
  Purchase #5 $230.88   5.778%   $244.2202   $244.22   $244.20   $244.20  
  Purchase #6 $187.28   5.303%   $197.2115   $197.21   $197.20   $197.20  
  Purchase #7 $234.55   12.307%   $263.4161   $263.42   $263.40   $263.40  
  7 purchase totals = $1,154.29       $1,247.2428   $1,247.24   $1,247.20   $1,247.30