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 $39.31   9.759%   $43.1463   $43.15   $43.15   $43.10  
  Purchase #2 $235.64   12.459%   $264.9984   $265.00   $265.00   $265.00  
  Purchase #3 $135.85   5.674%   $143.5581   $143.56   $143.55   $143.60  
  Purchase #4 $62.95   13.352%   $71.3551   $71.36   $71.35   $71.40  
  Purchase #5 $151.86   9.751%   $166.6679   $166.67   $166.65   $166.70  
  Purchase #6 $213.58   9.630%   $234.1478   $234.15   $234.15   $234.10  
  Purchase #7 $170.84   12.298%   $191.8499   $191.85   $191.85   $191.80  
  7 purchase totals = $1,010.03       $1,115.7235   $1,115.74   $1,115.70   $1,115.70