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 $58.50   12.550%   $65.8418   $65.84   $65.85   $65.80  
  Purchase #2 $228.67   5.564%   $241.3932   $241.39   $241.40   $241.40  
  Purchase #3 $62.47   3.715%   $64.7908   $64.79   $64.80   $64.80  
  Purchase #4 $171.67   7.229%   $184.08   $184.08   $184.10   $184.10  
  Purchase #5 $134.50   6.649%   $143.4429   $143.44   $143.45   $143.40  
  Purchase #6 $152.55   12.569%   $171.724   $171.72   $171.70   $171.70  
  Purchase #7 $244.78   10.572%   $270.6581   $270.66   $270.65   $270.70  
  7 purchase totals = $1,053.14       $1,141.9308   $1,141.92   $1,141.95   $1,141.90