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 $202.82   10.281%   $223.6719   $223.67   $223.65   $223.70  
  Purchase #2 $204.95   3.730%   $212.5946   $212.59   $212.60   $212.60  
  Purchase #3 $245.65   13.789%   $279.5227   $279.52   $279.50   $279.50  
  Purchase #4 $52.56   4.785%   $55.075   $55.08   $55.10   $55.10  
  Purchase #5 $57.58   4.258%   $60.0318   $60.03   $60.05   $60.00  
  Purchase #6 $160.76   4.656%   $168.245   $168.25   $168.25   $168.20  
  Purchase #7 $109.97   9.433%   $120.3435   $120.34   $120.35   $120.30  
  7 purchase totals = $1,034.29       $1,119.4845   $1,119.48   $1,119.50   $1,119.40