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 $34.98   4.787%   $36.6545   $36.65   $36.65   $36.70  
  Purchase #2 $97.48   6.133%   $103.4584   $103.46   $103.45   $103.50  
  Purchase #3 $201.69   10.730%   $223.3313   $223.33   $223.35   $223.30  
  Purchase #4 $80.41   8.736%   $87.4346   $87.43   $87.45   $87.40  
  Purchase #5 $71.73   8.221%   $77.6269   $77.63   $77.65   $77.60  
  Purchase #6 $245.87   8.111%   $265.8125   $265.81   $265.80   $265.80  
  Purchase #7 $199.64   6.596%   $212.8083   $212.81   $212.80   $212.80  
  7 purchase totals = $931.80       $1,007.1265   $1,007.12   $1,007.15   $1,007.10