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 $162.59   13.282%   $184.1852   $184.19   $184.20   $184.20  
  Purchase #2 $238.44   3.196%   $246.0605   $246.06   $246.05   $246.10  
  Purchase #3 $80.42   8.744%   $87.4519   $87.45   $87.45   $87.50  
  Purchase #4 $212.49   9.386%   $232.4343   $232.43   $232.45   $232.40  
  Purchase #5 $60.97   8.579%   $66.2006   $66.20   $66.20   $66.20  
  Purchase #6 $26.43   4.103%   $27.5144   $27.51   $27.50   $27.50  
  Purchase #7 $226.63   6.122%   $240.5043   $240.50   $240.50   $240.50  
  7 purchase totals = $1,007.97       $1,084.3512   $1,084.34   $1,084.35   $1,084.40