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 $46.99   6.585%   $50.0843   $50.08   $50.10   $50.10  
  Purchase #2 $155.31   3.491%   $160.7319   $160.73   $160.75   $160.70  
  Purchase #3 $223.34   3.690%   $231.5812   $231.58   $231.60   $231.60  
  Purchase #4 $61.36   10.817%   $67.9973   $68.00   $68.00   $68.00  
  Purchase #5 $171.29   8.125%   $185.2073   $185.21   $185.20   $185.20  
  Purchase #6 $203.30   8.707%   $221.0013   $221.00   $221.00   $221.00  
  Purchase #7 $176.43   8.822%   $191.9947   $191.99   $192.00   $192.00  
  7 purchase totals = $1,038.02       $1,108.5980   $1,108.59   $1,108.65   $1,108.60