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 $184.64   4.326%   $192.6275   $192.63   $192.65   $192.60  
  Purchase #2 $102.72   3.378%   $106.1899   $106.19   $106.20   $106.20  
  Purchase #3 $130.69   8.202%   $141.4092   $141.41   $141.40   $141.40  
  Purchase #4 $16.51   4.220%   $17.2067   $17.21   $17.20   $17.20  
  Purchase #5 $135.55   12.219%   $152.1129   $152.11   $152.10   $152.10  
  Purchase #6 $183.62   11.453%   $204.65   $204.65   $204.65   $204.70  
  Purchase #7 $11.84   12.541%   $13.3249   $13.32   $13.30   $13.30  
  7 purchase totals = $765.57       $827.5211   $827.52   $827.50   $827.50