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 $88.29   5.861%   $93.4647   $93.46   $93.45   $93.50  
  Purchase #2 $204.77   3.279%   $211.4844   $211.48   $211.50   $211.50  
  Purchase #3 $240.57   12.719%   $271.1681   $271.17   $271.15   $271.20  
  Purchase #4 $25.65   8.106%   $27.7292   $27.73   $27.75   $27.70  
  Purchase #5 $125.99   4.756%   $131.9821   $131.98   $132.00   $132.00  
  Purchase #6 $238.29   13.163%   $269.6561   $269.66   $269.65   $269.70  
  Purchase #7 $205.29   3.623%   $212.7277   $212.73   $212.75   $212.70  
  7 purchase totals = $1,128.85       $1,218.2123   $1,218.21   $1,218.25   $1,218.30