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 $111.48   11.867%   $124.7093   $124.71   $124.70   $124.70  
  Purchase #2 $205.94   13.562%   $233.8696   $233.87   $233.85   $233.90  
  Purchase #3 $62.73   9.471%   $68.6712   $68.67   $68.65   $68.70  
  Purchase #4 $161.40   8.119%   $174.5041   $174.50   $174.50   $174.50  
  Purchase #5 $176.25   7.369%   $189.2379   $189.24   $189.25   $189.20  
  Purchase #6 $196.72   13.170%   $222.628   $222.63   $222.65   $222.60  
  Purchase #7 $23.32   3.174%   $24.0602   $24.06   $24.05   $24.10  
  7 purchase totals = $937.84       $1,037.6803   $1,037.68   $1,037.65   $1,037.70