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 $129.47   13.541%   $147.0015   $147.00   $147.00   $147.00  
  Purchase #2 $189.26   12.415%   $212.7566   $212.76   $212.75   $212.80  
  Purchase #3 $134.56   13.184%   $152.3004   $152.30   $152.30   $152.30  
  Purchase #4 $241.60   13.867%   $275.1027   $275.10   $275.10   $275.10  
  Purchase #5 $21.34   9.138%   $23.29   $23.29   $23.30   $23.30  
  Purchase #6 $95.65   11.682%   $106.8238   $106.82   $106.80   $106.80  
  Purchase #7 $153.87   3.270%   $158.9015   $158.90   $158.90   $158.90  
  7 purchase totals = $965.75       $1,076.1765   $1,076.17   $1,076.15   $1,076.20