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 $196.55   3.426%   $203.2838   $203.28   $203.30   $203.30  
  Purchase #2 $232.51   6.122%   $246.7443   $246.74   $246.75   $246.70  
  Purchase #3 $54.71   8.392%   $59.3013   $59.30   $59.30   $59.30  
  Purchase #4 $246.47   8.336%   $267.0157   $267.02   $267.00   $267.00  
  Purchase #5 $153.29   3.555%   $158.7395   $158.74   $158.75   $158.70  
  Purchase #6 $179.87   12.171%   $201.762   $201.76   $201.75   $201.80  
  Purchase #7 $93.47   6.241%   $99.3035   $99.30   $99.30   $99.30  
  7 purchase totals = $1,156.87       $1,236.1501   $1,236.14   $1,236.15   $1,236.10