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 $94.86   11.842%   $106.0933   $106.09   $106.10   $106.10  
  Purchase #2 $170.33   6.155%   $180.8138   $180.81   $180.80   $180.80  
  Purchase #3 $42.39   6.497%   $45.1441   $45.14   $45.15   $45.10  
  Purchase #4 $128.30   9.519%   $140.5129   $140.51   $140.50   $140.50  
  Purchase #5 $90.42   5.297%   $95.2095   $95.21   $95.20   $95.20  
  Purchase #6 $214.47   7.400%   $230.3408   $230.34   $230.35   $230.30  
  Purchase #7 $209.32   12.106%   $234.6603   $234.66   $234.65   $234.70  
  7 purchase totals = $950.09       $1,032.7747   $1,032.76   $1,032.75   $1,032.70