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 $24.65   4.613%   $25.7871   $25.79   $25.80   $25.80  
  Purchase #2 $198.88   12.568%   $223.8752   $223.88   $223.90   $223.90  
  Purchase #3 $204.25   11.395%   $227.5243   $227.52   $227.50   $227.50  
  Purchase #4 $52.81   6.382%   $56.1803   $56.18   $56.20   $56.20  
  Purchase #5 $42.91   10.713%   $47.5069   $47.51   $47.50   $47.50  
  Purchase #6 $188.61   7.701%   $203.1349   $203.13   $203.15   $203.10  
  Purchase #7 $225.91   9.229%   $246.7592   $246.76   $246.75   $246.80  
  7 purchase totals = $938.02       $1,030.7679   $1,030.77   $1,030.80   $1,030.80