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 $204.52   10.416%   $225.8228   $225.82   $225.80   $225.80  
  Purchase #2 $239.76   6.407%   $255.1214   $255.12   $255.10   $255.10  
  Purchase #3 $24.45   9.364%   $26.7395   $26.74   $26.75   $26.70  
  Purchase #4 $159.85   7.346%   $171.5926   $171.59   $171.60   $171.60  
  Purchase #5 $65.82   3.574%   $68.1724   $68.17   $68.15   $68.20  
  Purchase #6 $69.80   7.374%   $74.9471   $74.95   $74.95   $74.90  
  Purchase #7 $224.31   11.506%   $250.1191   $250.12   $250.10   $250.10  
  7 purchase totals = $988.51       $1,072.5149   $1,072.51   $1,072.45   $1,072.40