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 $36.66   13.580%   $41.6384   $41.64   $41.65   $41.60  
  Purchase #2 $110.93   4.439%   $115.8542   $115.85   $115.85   $115.90  
  Purchase #3 $60.41   5.286%   $63.6033   $63.60   $63.60   $63.60  
  Purchase #4 $193.94   9.472%   $212.31   $212.31   $212.30   $212.30  
  Purchase #5 $176.47   9.158%   $192.6311   $192.63   $192.65   $192.60  
  Purchase #6 $150.86   6.441%   $160.5769   $160.58   $160.60   $160.60  
  Purchase #7 $149.96   12.240%   $168.3151   $168.32   $168.30   $168.30  
  7 purchase totals = $879.23       $954.9290   $954.93   $954.95   $954.90