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 $247.61   8.134%   $267.7506   $267.75   $267.75   $267.80  
  Purchase #2 $128.47   10.124%   $141.4763   $141.48   $141.50   $141.50  
  Purchase #3 $211.66   9.119%   $230.9613   $230.96   $230.95   $231.00  
  Purchase #4 $82.70   9.459%   $90.5226   $90.52   $90.50   $90.50  
  Purchase #5 $204.88   6.758%   $218.7258   $218.73   $218.75   $218.70  
  Purchase #6 $44.72   4.357%   $46.6685   $46.67   $46.65   $46.70  
  Purchase #7 $147.43   4.205%   $153.6294   $153.63   $153.65   $153.60  
  7 purchase totals = $1,067.47       $1,149.7345   $1,149.74   $1,149.75   $1,149.80