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 $53.96   9.446%   $59.0571   $59.06   $59.05   $59.10  
  Purchase #2 $130.32   13.281%   $147.6278   $147.63   $147.65   $147.60  
  Purchase #3 $99.70   10.666%   $110.334   $110.33   $110.35   $110.30  
  Purchase #4 $125.96   9.372%   $137.765   $137.77   $137.75   $137.80  
  Purchase #5 $205.93   12.450%   $231.5683   $231.57   $231.55   $231.60  
  Purchase #6 $185.48   11.251%   $206.3484   $206.35   $206.35   $206.30  
  Purchase #7 $176.51   12.297%   $198.2154   $198.22   $198.20   $198.20  
  7 purchase totals = $977.86       $1,090.9160   $1,090.93   $1,090.90   $1,090.90