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 $187.35   6.282%   $199.1193   $199.12   $199.10   $199.10  
  Purchase #2 $193.67   7.728%   $208.6368   $208.64   $208.65   $208.60  
  Purchase #3 $71.76   12.751%   $80.9101   $80.91   $80.90   $80.90  
  Purchase #4 $88.49   7.734%   $95.3338   $95.33   $95.35   $95.30  
  Purchase #5 $199.60   13.573%   $226.6917   $226.69   $226.70   $226.70  
  Purchase #6 $77.78   9.678%   $85.3075   $85.31   $85.30   $85.30  
  Purchase #7 $219.49   5.685%   $231.968   $231.97   $231.95   $232.00  
  7 purchase totals = $1,038.14       $1,127.9672   $1,127.97   $1,127.95   $1,127.90