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 $58.56   3.708%   $60.7314   $60.73   $60.75   $60.70  
  Purchase #2 $236.32   6.246%   $251.0805   $251.08   $251.10   $251.10  
  Purchase #3 $66.72   9.469%   $73.0377   $73.04   $73.05   $73.00  
  Purchase #4 $61.36   9.668%   $67.2923   $67.29   $67.30   $67.30  
  Purchase #5 $241.93   11.338%   $269.36   $269.36   $269.35   $269.40  
  Purchase #6 $250.30   9.600%   $274.3288   $274.33   $274.35   $274.30  
  Purchase #7 $219.25   12.747%   $247.1978   $247.20   $247.20   $247.20  
  7 purchase totals = $1,134.44       $1,243.0285   $1,243.03   $1,243.10   $1,243.00