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 $231.36   9.867%   $254.1883   $254.19   $254.20   $254.20  
  Purchase #2 $168.73   9.361%   $184.5248   $184.52   $184.50   $184.50  
  Purchase #3 $68.77   9.770%   $75.4888   $75.49   $75.50   $75.50  
  Purchase #4 $94.92   6.424%   $101.0177   $101.02   $101.00   $101.00  
  Purchase #5 $61.83   8.378%   $67.0101   $67.01   $67.00   $67.00  
  Purchase #6 $87.80   9.419%   $96.0699   $96.07   $96.05   $96.10  
  Purchase #7 $206.30   11.544%   $230.1153   $230.12   $230.10   $230.10  
  7 purchase totals = $919.71       $1,008.4149   $1,008.42   $1,008.35   $1,008.40