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 $134.98   12.831%   $152.2993   $152.30   $152.30   $152.30  
  Purchase #2 $243.88   7.408%   $261.9466   $261.95   $261.95   $261.90  
  Purchase #3 $141.56   6.625%   $150.9384   $150.94   $150.95   $150.90  
  Purchase #4 $212.36   9.130%   $231.7485   $231.75   $231.75   $231.70  
  Purchase #5 $186.94   13.582%   $212.3302   $212.33   $212.35   $212.30  
  Purchase #6 $62.38   3.505%   $64.5664   $64.57   $64.55   $64.60  
  Purchase #7 $15.81   7.267%   $16.9589   $16.96   $16.95   $17.00  
  7 purchase totals = $997.91       $1,090.7883   $1,090.80   $1,090.80   $1,090.70