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 $55.57   6.613%   $59.2448   $59.24   $59.25   $59.20  
  Purchase #2 $195.27   8.835%   $212.5221   $212.52   $212.50   $212.50  
  Purchase #3 $145.32   8.165%   $157.1854   $157.19   $157.20   $157.20  
  Purchase #4 $231.93   13.740%   $263.7972   $263.80   $263.80   $263.80  
  Purchase #5 $167.76   6.409%   $178.5117   $178.51   $178.50   $178.50  
  Purchase #6 $12.88   11.514%   $14.363   $14.36   $14.35   $14.40  
  Purchase #7 $54.56   11.215%   $60.6789   $60.68   $60.70   $60.70  
  7 purchase totals = $863.29       $946.3031   $946.30   $946.30   $946.30