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 $164.70   4.634%   $172.3322   $172.33   $172.35   $172.30  
  Purchase #2 $36.72   6.469%   $39.0954   $39.10   $39.10   $39.10  
  Purchase #3 $211.71   8.108%   $228.8754   $228.88   $228.90   $228.90  
  Purchase #4 $173.51   9.199%   $189.4712   $189.47   $189.45   $189.50  
  Purchase #5 $75.27   9.148%   $82.1557   $82.16   $82.15   $82.20  
  Purchase #6 $72.65   12.836%   $81.9754   $81.98   $82.00   $82.00  
  Purchase #7 $102.74   5.728%   $108.6249   $108.62   $108.60   $108.60  
  7 purchase totals = $837.30       $902.5302   $902.54   $902.55   $902.60