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 $80.76   8.263%   $87.4332   $87.43   $87.45   $87.40  
  Purchase #2 $249.79   9.116%   $272.5609   $272.56   $272.55   $272.60  
  Purchase #3 $53.83   4.427%   $56.2131   $56.21   $56.20   $56.20  
  Purchase #4 $22.93   5.848%   $24.2709   $24.27   $24.25   $24.30  
  Purchase #5 $183.65   6.159%   $194.961   $194.96   $194.95   $195.00  
  Purchase #6 $150.83   3.755%   $156.4937   $156.49   $156.50   $156.50  
  Purchase #7 $22.77   11.678%   $25.4291   $25.43   $25.45   $25.40  
  7 purchase totals = $764.56       $817.3619   $817.35   $817.35   $817.40