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 $43.89   13.560%   $49.8415   $49.84   $49.85   $49.80  
  Purchase #2 $246.81   10.842%   $273.5691   $273.57   $273.55   $273.60  
  Purchase #3 $135.96   10.795%   $150.6369   $150.64   $150.65   $150.60  
  Purchase #4 $174.63   9.709%   $191.5848   $191.58   $191.60   $191.60  
  Purchase #5 $211.87   6.671%   $226.0038   $226.00   $226.00   $226.00  
  Purchase #6 $25.78   7.183%   $27.6318   $27.63   $27.65   $27.60  
  Purchase #7 $229.35   5.103%   $241.0537   $241.05   $241.05   $241.10  
  7 purchase totals = $1,068.29       $1,160.3216   $1,160.31   $1,160.35   $1,160.30