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 $195.48   9.632%   $214.3086   $214.31   $214.30   $214.30  
  Purchase #2 $149.63   3.818%   $155.3429   $155.34   $155.35   $155.30  
  Purchase #3 $116.68   4.642%   $122.0963   $122.10   $122.10   $122.10  
  Purchase #4 $216.89   4.458%   $226.559   $226.56   $226.55   $226.60  
  Purchase #5 $95.70   12.511%   $107.673   $107.67   $107.65   $107.70  
  Purchase #6 $77.46   9.523%   $84.8365   $84.84   $84.85   $84.80  
  Purchase #7 $160.33   12.746%   $180.7657   $180.77   $180.75   $180.80  
  7 purchase totals = $1,012.17       $1,091.5820   $1,091.59   $1,091.55   $1,091.60