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 $92.29   4.156%   $96.1256   $96.13   $96.15   $96.10  
  Purchase #2 $233.46   4.795%   $244.6544   $244.65   $244.65   $244.70  
  Purchase #3 $231.78   5.723%   $245.0448   $245.04   $245.05   $245.00  
  Purchase #4 $27.63   11.637%   $30.8453   $30.85   $30.85   $30.80  
  Purchase #5 $132.32   13.575%   $150.2824   $150.28   $150.30   $150.30  
  Purchase #6 $77.97   11.722%   $87.1096   $87.11   $87.10   $87.10  
  Purchase #7 $142.28   3.600%   $147.4021   $147.40   $147.40   $147.40  
  7 purchase totals = $937.73       $1,001.4642   $1,001.46   $1,001.50   $1,001.40