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 $130.96   7.648%   $140.9758   $140.98   $141.00   $141.00  
  Purchase #2 $211.89   11.221%   $235.6662   $235.67   $235.65   $235.70  
  Purchase #3 $73.42   3.113%   $75.7056   $75.71   $75.70   $75.70  
  Purchase #4 $173.48   4.372%   $181.0645   $181.06   $181.05   $181.10  
  Purchase #5 $76.95   10.769%   $85.2367   $85.24   $85.25   $85.20  
  Purchase #6 $99.99   5.816%   $105.8054   $105.81   $105.80   $105.80  
  Purchase #7 $212.74   6.642%   $226.8702   $226.87   $226.85   $226.90  
  7 purchase totals = $979.43       $1,051.3244   $1,051.34   $1,051.30   $1,051.40