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 $218.61   12.666%   $246.2991   $246.30   $246.30   $246.30  
  Purchase #2 $130.43   12.628%   $146.9007   $146.90   $146.90   $146.90  
  Purchase #3 $34.64   13.856%   $39.4397   $39.44   $39.45   $39.40  
  Purchase #4 $173.78   12.424%   $195.3704   $195.37   $195.35   $195.40  
  Purchase #5 $160.79   11.711%   $179.6201   $179.62   $179.60   $179.60  
  Purchase #6 $220.67   4.333%   $230.2316   $230.23   $230.25   $230.20  
  Purchase #7 $114.55   5.332%   $120.6578   $120.66   $120.65   $120.70  
  7 purchase totals = $1,053.47       $1,158.5194   $1,158.52   $1,158.50   $1,158.50