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 $145.94   6.243%   $155.051   $155.05   $155.05   $155.10  
  Purchase #2 $209.80   13.615%   $238.3643   $238.36   $238.35   $238.40  
  Purchase #3 $121.78   11.755%   $136.0952   $136.10   $136.10   $136.10  
  Purchase #4 $232.32   9.354%   $254.0512   $254.05   $254.05   $254.10  
  Purchase #5 $60.33   8.801%   $65.6396   $65.64   $65.65   $65.60  
  Purchase #6 $118.68   8.273%   $128.4984   $128.50   $128.50   $128.50  
  Purchase #7 $119.35   3.662%   $123.7206   $123.72   $123.70   $123.70  
  7 purchase totals = $1,008.20       $1,101.4203   $1,101.42   $1,101.40   $1,101.50