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 $94.68   8.475%   $102.7041   $102.70   $102.70   $102.70  
  Purchase #2 $174.68   3.741%   $181.2148   $181.21   $181.20   $181.20  
  Purchase #3 $124.28   11.373%   $138.4144   $138.41   $138.40   $138.40  
  Purchase #4 $188.80   7.295%   $202.573   $202.57   $202.55   $202.60  
  Purchase #5 $23.76   9.133%   $25.93   $25.93   $25.95   $25.90  
  Purchase #6 $108.59   10.179%   $119.6434   $119.64   $119.65   $119.60  
  Purchase #7 $224.85   10.420%   $248.2794   $248.28   $248.30   $248.30  
  7 purchase totals = $939.64       $1,018.7591   $1,018.74   $1,018.75   $1,018.70