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 $182.52   8.264%   $197.6035   $197.60   $197.60   $197.60  
  Purchase #2 $114.72   9.589%   $125.7205   $125.72   $125.70   $125.70  
  Purchase #3 $205.55   5.351%   $216.549   $216.55   $216.55   $216.50  
  Purchase #4 $37.28   12.240%   $41.8431   $41.84   $41.85   $41.80  
  Purchase #5 $118.51   13.363%   $134.3465   $134.35   $134.35   $134.30  
  Purchase #6 $215.87   10.798%   $239.1796   $239.18   $239.20   $239.20  
  Purchase #7 $35.84   11.155%   $39.838   $39.84   $39.85   $39.80  
  7 purchase totals = $910.29       $995.0802   $995.08   $995.10   $994.90