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 $58.34   9.540%   $63.9056   $63.91   $63.90   $63.90  
  Purchase #2 $94.28   11.184%   $104.8243   $104.82   $104.80   $104.80  
  Purchase #3 $221.43   3.173%   $228.456   $228.46   $228.45   $228.50  
  Purchase #4 $216.58   11.352%   $241.1662   $241.17   $241.15   $241.20  
  Purchase #5 $127.96   6.267%   $135.9793   $135.98   $136.00   $136.00  
  Purchase #6 $183.37   6.201%   $194.7408   $194.74   $194.75   $194.70  
  Purchase #7 $77.79   6.221%   $82.6293   $82.63   $82.65   $82.60  
  7 purchase totals = $979.75       $1,051.7015   $1,051.71   $1,051.70   $1,051.70