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 $207.98   7.167%   $222.8859   $222.89   $222.90   $222.90  
  Purchase #2 $216.45   4.823%   $226.8894   $226.89   $226.90   $226.90  
  Purchase #3 $24.67   9.506%   $27.0151   $27.02   $27.00   $27.00  
  Purchase #4 $196.47   9.249%   $214.6415   $214.64   $214.65   $214.60  
  Purchase #5 $159.45   8.453%   $172.9283   $172.93   $172.95   $172.90  
  Purchase #6 $220.45   11.371%   $245.5174   $245.52   $245.50   $245.50  
  Purchase #7 $21.79   4.851%   $22.847   $22.85   $22.85   $22.80  
  7 purchase totals = $1,047.26       $1,132.7246   $1,132.74   $1,132.75   $1,132.60