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 $192.39   6.441%   $204.7818   $204.78   $204.80   $204.80  
  Purchase #2 $6.57   5.850%   $6.9543   $6.95   $6.95   $7.00  
  Purchase #3 $56.55   7.547%   $60.8178   $60.82   $60.80   $60.80  
  Purchase #4 $208.58   11.706%   $232.9964   $233.00   $233.00   $233.00  
  Purchase #5 $28.32   3.200%   $29.2262   $29.23   $29.25   $29.20  
  Purchase #6 $194.42   10.169%   $214.1906   $214.19   $214.20   $214.20  
  Purchase #7 $174.84   9.559%   $191.553   $191.55   $191.55   $191.60  
  7 purchase totals = $861.67       $940.5201   $940.52   $940.55   $940.60