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 $60.52   9.433%   $66.2289   $66.23   $66.25   $66.20  
  Purchase #2 $167.96   6.350%   $178.6255   $178.63   $178.65   $178.60  
  Purchase #3 $133.51   7.397%   $143.3857   $143.39   $143.40   $143.40  
  Purchase #4 $74.61   12.188%   $83.7035   $83.70   $83.70   $83.70  
  Purchase #5 $238.31   5.736%   $251.9795   $251.98   $252.00   $252.00  
  Purchase #6 $84.30   5.605%   $89.025   $89.03   $89.05   $89.00  
  Purchase #7 $144.51   7.340%   $155.117   $155.12   $155.10   $155.10  
  7 purchase totals = $903.72       $968.0651   $968.08   $968.15   $968.00