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 $53.37   12.357%   $59.9649   $59.96   $59.95   $60.00  
  Purchase #2 $75.40   9.453%   $82.5276   $82.53   $82.55   $82.50  
  Purchase #3 $24.86   8.568%   $26.99   $26.99   $27.00   $27.00  
  Purchase #4 $211.97   3.494%   $219.3762   $219.38   $219.40   $219.40  
  Purchase #5 $160.94   8.740%   $175.0062   $175.01   $175.00   $175.00  
  Purchase #6 $201.47   4.509%   $210.5543   $210.55   $210.55   $210.60  
  Purchase #7 $243.77   13.186%   $275.9135   $275.91   $275.90   $275.90  
  7 purchase totals = $971.78       $1,050.3327   $1,050.33   $1,050.35   $1,050.40