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 $59.35   11.714%   $66.3023   $66.30   $66.30   $66.30  
  Purchase #2 $102.27   6.230%   $108.6414   $108.64   $108.65   $108.60  
  Purchase #3 $122.57   10.424%   $135.3467   $135.35   $135.35   $135.30  
  Purchase #4 $209.48   10.482%   $231.4377   $231.44   $231.45   $231.40  
  Purchase #5 $44.65   5.868%   $47.2701   $47.27   $47.25   $47.30  
  Purchase #6 $147.53   13.392%   $167.2872   $167.29   $167.30   $167.30  
  Purchase #7 $14.71   10.331%   $16.2297   $16.23   $16.25   $16.20  
  7 purchase totals = $700.56       $772.5151   $772.52   $772.55   $772.40