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 $204.82   11.110%   $227.5755   $227.58   $227.60   $227.60  
  Purchase #2 $223.93   10.689%   $247.8659   $247.87   $247.85   $247.90  
  Purchase #3 $10.42   6.192%   $11.0652   $11.07   $11.05   $11.10  
  Purchase #4 $163.29   7.218%   $175.0763   $175.08   $175.10   $175.10  
  Purchase #5 $218.65   11.119%   $242.9617   $242.96   $242.95   $243.00  
  Purchase #6 $100.67   6.317%   $107.0293   $107.03   $107.05   $107.00  
  Purchase #7 $9.96   9.502%   $10.9064   $10.91   $10.90   $10.90  
  7 purchase totals = $931.74       $1,022.4803   $1,022.50   $1,022.50   $1,022.60