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 $176.75   9.836%   $194.1351   $194.14   $194.15   $194.10  
  Purchase #2 $218.88   12.561%   $246.3735   $246.37   $246.35   $246.40  
  Purchase #3 $190.73   6.575%   $203.2705   $203.27   $203.25   $203.30  
  Purchase #4 $117.53   13.717%   $133.6516   $133.65   $133.65   $133.70  
  Purchase #5 $55.77   10.444%   $61.5946   $61.59   $61.60   $61.60  
  Purchase #6 $53.54   9.735%   $58.7521   $58.75   $58.75   $58.80  
  Purchase #7 $120.67   6.617%   $128.6547   $128.65   $128.65   $128.70  
  7 purchase totals = $933.87       $1,026.4321   $1,026.42   $1,026.40   $1,026.60