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 $108.39   10.546%   $119.8208   $119.82   $119.80   $119.80  
  Purchase #2 $181.52   13.855%   $206.6696   $206.67   $206.65   $206.70  
  Purchase #3 $74.56   8.573%   $80.952   $80.95   $80.95   $81.00  
  Purchase #4 $248.70   13.270%   $281.7025   $281.70   $281.70   $281.70  
  Purchase #5 $48.90   6.143%   $51.9039   $51.90   $51.90   $51.90  
  Purchase #6 $92.86   12.790%   $104.7368   $104.74   $104.75   $104.70  
  Purchase #7 $156.31   5.493%   $164.8961   $164.90   $164.90   $164.90  
  7 purchase totals = $911.24       $1,010.6817   $1,010.68   $1,010.65   $1,010.70