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 $79.37   8.772%   $86.3323   $86.33   $86.35   $86.30  
  Purchase #2 $184.95   9.520%   $202.5572   $202.56   $202.55   $202.60  
  Purchase #3 $204.65   8.179%   $221.3883   $221.39   $221.40   $221.40  
  Purchase #4 $168.26   4.159%   $175.2579   $175.26   $175.25   $175.30  
  Purchase #5 $225.68   11.364%   $251.3263   $251.33   $251.35   $251.30  
  Purchase #6 $67.97   8.818%   $73.9636   $73.96   $73.95   $74.00  
  Purchase #7 $210.68   6.611%   $224.6081   $224.61   $224.60   $224.60  
  7 purchase totals = $1,141.56       $1,235.4337   $1,235.44   $1,235.45   $1,235.50