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 $55.92   7.253%   $59.9759   $59.98   $60.00   $60.00  
  Purchase #2 $147.25   10.479%   $162.6803   $162.68   $162.70   $162.70  
  Purchase #3 $193.61   3.666%   $200.7077   $200.71   $200.70   $200.70  
  Purchase #4 $162.26   3.378%   $167.7411   $167.74   $167.75   $167.70  
  Purchase #5 $100.40   10.259%   $110.7   $110.70   $110.70   $110.70  
  Purchase #6 $86.96   11.434%   $96.903   $96.90   $96.90   $96.90  
  Purchase #7 $187.57   11.698%   $209.5119   $209.51   $209.50   $209.50  
  7 purchase totals = $933.97       $1,008.2199   $1,008.22   $1,008.25   $1,008.20