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 $188.86   13.575%   $214.4977   $214.50   $214.50   $214.50  
  Purchase #2 $192.57   6.236%   $204.5787   $204.58   $204.60   $204.60  
  Purchase #3 $20.60   3.858%   $21.3947   $21.39   $21.40   $21.40  
  Purchase #4 $226.37   11.294%   $251.9362   $251.94   $251.95   $251.90  
  Purchase #5 $221.61   11.734%   $247.6137   $247.61   $247.60   $247.60  
  Purchase #6 $53.85   10.533%   $59.522   $59.52   $59.50   $59.50  
  Purchase #7 $119.75   9.120%   $130.6712   $130.67   $130.65   $130.70  
  7 purchase totals = $1,023.61       $1,130.2142   $1,130.21   $1,130.20   $1,130.20