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 $32.84   13.595%   $37.3046   $37.30   $37.30   $37.30  
  Purchase #2 $163.74   6.648%   $174.6254   $174.63   $174.65   $174.60  
  Purchase #3 $193.33   5.511%   $203.9844   $203.98   $204.00   $204.00  
  Purchase #4 $226.59   11.477%   $252.5957   $252.60   $252.60   $252.60  
  Purchase #5 $161.84   5.658%   $170.9969   $171.00   $171.00   $171.00  
  Purchase #6 $209.83   11.825%   $234.6424   $234.64   $234.65   $234.60  
  Purchase #7 $156.47   10.735%   $173.2671   $173.27   $173.25   $173.30  
  7 purchase totals = $1,144.64       $1,247.4165   $1,247.42   $1,247.45   $1,247.40