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 $88.88   11.524%   $99.1225   $99.12   $99.10   $99.10  
  Purchase #2 $161.72   3.659%   $167.6373   $167.64   $167.65   $167.60  
  Purchase #3 $148.32   10.711%   $164.2066   $164.21   $164.20   $164.20  
  Purchase #4 $226.35   9.467%   $247.7786   $247.78   $247.80   $247.80  
  Purchase #5 $153.80   5.197%   $161.793   $161.79   $161.80   $161.80  
  Purchase #6 $182.74   4.810%   $191.5298   $191.53   $191.55   $191.50  
  Purchase #7 $34.83   10.743%   $38.5718   $38.57   $38.55   $38.60  
  7 purchase totals = $996.64       $1,070.6396   $1,070.64   $1,070.65   $1,070.60