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 $115.55   3.531%   $119.6301   $119.63   $119.65   $119.60  
  Purchase #2 $100.96   12.255%   $113.3326   $113.33   $113.35   $113.30  
  Purchase #3 $60.94   7.203%   $65.3295   $65.33   $65.35   $65.30  
  Purchase #4 $74.75   11.252%   $83.1609   $83.16   $83.15   $83.20  
  Purchase #5 $223.90   3.370%   $231.4454   $231.45   $231.45   $231.40  
  Purchase #6 $180.85   3.401%   $187.0007   $187.00   $187.00   $187.00  
  Purchase #7 $162.52   5.681%   $171.7528   $171.75   $171.75   $171.80  
  7 purchase totals = $919.47       $971.6520   $971.65   $971.70   $971.60