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 $84.66   3.112%   $87.2946   $87.29   $87.30   $87.30  
  Purchase #2 $202.25   13.723%   $230.0048   $230.00   $230.00   $230.00  
  Purchase #3 $250.95   8.774%   $272.9684   $272.97   $272.95   $273.00  
  Purchase #4 $186.98   12.120%   $209.642   $209.64   $209.65   $209.60  
  Purchase #5 $135.44   9.449%   $148.2377   $148.24   $148.25   $148.20  
  Purchase #6 $52.54   12.443%   $59.0776   $59.08   $59.10   $59.10  
  Purchase #7 $202.41   9.120%   $220.8698   $220.87   $220.85   $220.90  
  7 purchase totals = $1,115.23       $1,228.0949   $1,228.09   $1,228.10   $1,228.10