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 $37.51   9.354%   $41.0187   $41.02   $41.00   $41.00  
  Purchase #2 $189.87   11.832%   $212.3354   $212.34   $212.35   $212.30  
  Purchase #3 $78.53   6.451%   $83.596   $83.60   $83.60   $83.60  
  Purchase #4 $166.48   10.466%   $183.9038   $183.90   $183.90   $183.90  
  Purchase #5 $95.94   13.282%   $108.6828   $108.68   $108.70   $108.70  
  Purchase #6 $250.59   5.810%   $265.1493   $265.15   $265.15   $265.10  
  Purchase #7 $169.52   9.130%   $184.9972   $185.00   $185.00   $185.00  
  7 purchase totals = $988.44       $1,079.6832   $1,079.69   $1,079.70   $1,079.60