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 $98.88   12.198%   $110.9414   $110.94   $110.95   $110.90  
  Purchase #2 $244.50   7.416%   $262.6321   $262.63   $262.65   $262.60  
  Purchase #3 $153.65   7.714%   $165.5026   $165.50   $165.50   $165.50  
  Purchase #4 $173.96   4.488%   $181.7673   $181.77   $181.75   $181.80  
  Purchase #5 $33.47   4.671%   $35.0334   $35.03   $35.05   $35.00  
  Purchase #6 $40.65   7.767%   $43.8073   $43.81   $43.80   $43.80  
  Purchase #7 $188.52   8.117%   $203.8222   $203.82   $203.80   $203.80  
  7 purchase totals = $933.63       $1,003.5063   $1,003.50   $1,003.50   $1,003.40