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 $85.54   8.842%   $93.1034   $93.10   $93.10   $93.10  
  Purchase #2 $240.78   12.704%   $271.3687   $271.37   $271.35   $271.40  
  Purchase #3 $89.69   5.798%   $94.8902   $94.89   $94.90   $94.90  
  Purchase #4 $123.67   8.442%   $134.1102   $134.11   $134.10   $134.10  
  Purchase #5 $56.47   5.486%   $59.5679   $59.57   $59.55   $59.60  
  Purchase #6 $184.35   9.634%   $202.1103   $202.11   $202.10   $202.10  
  Purchase #7 $228.33   7.691%   $245.8909   $245.89   $245.90   $245.90  
  7 purchase totals = $1,008.83       $1,101.0416   $1,101.04   $1,101.00   $1,101.10