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 $232.98   13.439%   $264.2902   $264.29   $264.30   $264.30  
  Purchase #2 $77.81   7.411%   $83.5765   $83.58   $83.60   $83.60  
  Purchase #3 $190.70   10.835%   $211.3623   $211.36   $211.35   $211.40  
  Purchase #4 $114.57   7.651%   $123.3358   $123.34   $123.35   $123.30  
  Purchase #5 $160.27   13.320%   $181.618   $181.62   $181.60   $181.60  
  Purchase #6 $195.26   8.586%   $212.025   $212.03   $212.05   $212.00  
  Purchase #7 $111.88   4.385%   $116.7859   $116.79   $116.80   $116.80  
  7 purchase totals = $1,083.47       $1,192.9937   $1,193.01   $1,193.05   $1,193.00