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 $46.82   9.341%   $51.1935   $51.19   $51.20   $51.20  
  Purchase #2 $54.80   12.558%   $61.6818   $61.68   $61.70   $61.70  
  Purchase #3 $162.53   8.732%   $176.7221   $176.72   $176.70   $176.70  
  Purchase #4 $187.44   9.415%   $205.0875   $205.09   $205.10   $205.10  
  Purchase #5 $142.56   5.768%   $150.7829   $150.78   $150.80   $150.80  
  Purchase #6 $227.53   12.140%   $255.1521   $255.15   $255.15   $255.20  
  Purchase #7 $174.92   10.133%   $192.6446   $192.64   $192.65   $192.60  
  7 purchase totals = $996.60       $1,093.2645   $1,093.25   $1,093.30   $1,093.30