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 $56.65   7.817%   $61.0783   $61.08   $61.10   $61.10  
  Purchase #2 $141.78   10.659%   $156.8923   $156.89   $156.90   $156.90  
  Purchase #3 $65.55   12.428%   $73.6966   $73.70   $73.70   $73.70  
  Purchase #4 $219.32   5.377%   $231.1128   $231.11   $231.10   $231.10  
  Purchase #5 $112.79   12.795%   $127.2215   $127.22   $127.20   $127.20  
  Purchase #6 $82.94   11.217%   $92.2434   $92.24   $92.25   $92.20  
  Purchase #7 $132.65   4.539%   $138.671   $138.67   $138.65   $138.70  
  7 purchase totals = $811.68       $880.9159   $880.91   $880.90   $880.90