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 $54.44   10.274%   $60.0332   $60.03   $60.05   $60.00  
  Purchase #2 $205.27   3.245%   $211.931   $211.93   $211.95   $211.90  
  Purchase #3 $148.46   8.475%   $161.042   $161.04   $161.05   $161.00  
  Purchase #4 $25.50   8.294%   $27.615   $27.62   $27.60   $27.60  
  Purchase #5 $154.60   9.216%   $168.8479   $168.85   $168.85   $168.80  
  Purchase #6 $150.58   3.874%   $156.4135   $156.41   $156.40   $156.40  
  Purchase #7 $231.67   7.331%   $248.6537   $248.65   $248.65   $248.70  
  7 purchase totals = $970.52       $1,034.5363   $1,034.53   $1,034.55   $1,034.40