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 $69.71   5.451%   $73.5099   $73.51   $73.50   $73.50  
  Purchase #2 $96.41   7.283%   $103.4315   $103.43   $103.45   $103.40  
  Purchase #3 $241.33   9.111%   $263.3176   $263.32   $263.30   $263.30  
  Purchase #4 $237.36   5.595%   $250.6403   $250.64   $250.65   $250.60  
  Purchase #5 $8.35   5.659%   $8.8225   $8.82   $8.80   $8.80  
  Purchase #6 $94.60   12.846%   $106.7523   $106.75   $106.75   $106.80  
  Purchase #7 $193.68   4.115%   $201.6499   $201.65   $201.65   $201.60  
  7 purchase totals = $941.44       $1,008.1240   $1,008.12   $1,008.10   $1,008.00