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 $69.30   6.281%   $73.6527   $73.65   $73.65   $73.70  
  Purchase #2 $130.52   11.364%   $145.3523   $145.35   $145.35   $145.40  
  Purchase #3 $162.81   8.355%   $176.4128   $176.41   $176.40   $176.40  
  Purchase #4 $50.29   11.441%   $56.0437   $56.04   $56.05   $56.00  
  Purchase #5 $123.91   3.452%   $128.1874   $128.19   $128.20   $128.20  
  Purchase #6 $23.94   12.529%   $26.9394   $26.94   $26.95   $26.90  
  Purchase #7 $219.34   4.627%   $229.4889   $229.49   $229.50   $229.50  
  7 purchase totals = $780.11       $836.0772   $836.07   $836.10   $836.10