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 $131.87   10.144%   $145.2469   $145.25   $145.25   $145.20  
  Purchase #2 $203.54   4.508%   $212.7156   $212.72   $212.70   $212.70  
  Purchase #3 $79.48   9.704%   $87.1927   $87.19   $87.20   $87.20  
  Purchase #4 $137.49   13.834%   $156.5104   $156.51   $156.50   $156.50  
  Purchase #5 $68.75   9.235%   $75.0991   $75.10   $75.10   $75.10  
  Purchase #6 $250.88   5.314%   $264.2118   $264.21   $264.20   $264.20  
  Purchase #7 $121.76   3.468%   $125.9826   $125.98   $126.00   $126.00  
  7 purchase totals = $993.77       $1,066.9591   $1,066.96   $1,066.95   $1,066.90