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 $87.96   9.206%   $96.0576   $96.06   $96.05   $96.10  
  Purchase #2 $192.70   6.716%   $205.6417   $205.64   $205.65   $205.60  
  Purchase #3 $234.62   9.782%   $257.5705   $257.57   $257.55   $257.60  
  Purchase #4 $123.45   9.590%   $135.2889   $135.29   $135.30   $135.30  
  Purchase #5 $105.28   5.211%   $110.7661   $110.77   $110.75   $110.80  
  Purchase #6 $123.61   13.524%   $140.327   $140.33   $140.35   $140.30  
  Purchase #7 $117.67   11.405%   $131.0903   $131.09   $131.10   $131.10  
  7 purchase totals = $985.29       $1,076.7421   $1,076.75   $1,076.75   $1,076.80