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 $182.29   13.668%   $207.2054   $207.21   $207.20   $207.20  
  Purchase #2 $195.59   5.301%   $205.9582   $205.96   $205.95   $206.00  
  Purchase #3 $99.64   5.416%   $105.0365   $105.04   $105.05   $105.00  
  Purchase #4 $246.80   8.728%   $268.3407   $268.34   $268.35   $268.30  
  Purchase #5 $36.83   7.782%   $39.6961   $39.70   $39.70   $39.70  
  Purchase #6 $189.89   6.481%   $202.1968   $202.20   $202.20   $202.20  
  Purchase #7 $214.60   8.395%   $232.6157   $232.62   $232.60   $232.60  
  7 purchase totals = $1,165.64       $1,261.0494   $1,261.07   $1,261.05   $1,261.00