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 $184.57   10.351%   $203.6748   $203.67   $203.65   $203.70  
  Purchase #2 $9.81   7.296%   $10.5257   $10.53   $10.55   $10.50  
  Purchase #3 $106.54   5.614%   $112.5212   $112.52   $112.50   $112.50  
  Purchase #4 $227.57   7.791%   $245.3   $245.30   $245.30   $245.30  
  Purchase #5 $220.58   11.593%   $246.1518   $246.15   $246.15   $246.20  
  Purchase #6 $190.68   13.410%   $216.2502   $216.25   $216.25   $216.30  
  Purchase #7 $20.77   7.568%   $22.3419   $22.34   $22.35   $22.30  
  7 purchase totals = $960.52       $1,056.7656   $1,056.76   $1,056.75   $1,056.80