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 $226.59   12.248%   $254.3427   $254.34   $254.35   $254.30  
  Purchase #2 $70.72   5.670%   $74.7298   $74.73   $74.75   $74.70  
  Purchase #3 $39.51   11.453%   $44.0351   $44.04   $44.05   $44.00  
  Purchase #4 $145.57   4.753%   $152.4889   $152.49   $152.50   $152.50  
  Purchase #5 $250.53   3.452%   $259.1783   $259.18   $259.20   $259.20  
  Purchase #6 $186.80   4.614%   $195.419   $195.42   $195.40   $195.40  
  Purchase #7 $29.97   5.829%   $31.717   $31.72   $31.70   $31.70  
  7 purchase totals = $949.69       $1,011.9108   $1,011.92   $1,011.95   $1,011.80