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 $96.74   6.757%   $103.2767   $103.28   $103.30   $103.30  
  Purchase #2 $104.49   13.428%   $118.5209   $118.52   $118.50   $118.50  
  Purchase #3 $178.55   11.767%   $199.56   $199.56   $199.55   $199.60  
  Purchase #4 $69.53   7.685%   $74.8734   $74.87   $74.85   $74.90  
  Purchase #5 $38.48   3.759%   $39.9265   $39.93   $39.95   $39.90  
  Purchase #6 $239.60   5.424%   $252.5959   $252.60   $252.60   $252.60  
  Purchase #7 $210.47   6.294%   $223.717   $223.72   $223.70   $223.70  
  7 purchase totals = $937.86       $1,012.4704   $1,012.48   $1,012.45   $1,012.50