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 $57.40   4.217%   $59.8206   $59.82   $59.80   $59.80  
  Purchase #2 $212.74   11.714%   $237.6604   $237.66   $237.65   $237.70  
  Purchase #3 $85.62   6.676%   $91.336   $91.34   $91.35   $91.30  
  Purchase #4 $101.25   6.385%   $107.7148   $107.71   $107.70   $107.70  
  Purchase #5 $203.83   8.208%   $220.5604   $220.56   $220.55   $220.60  
  Purchase #6 $137.89   10.816%   $152.8042   $152.80   $152.80   $152.80  
  Purchase #7 $175.66   3.578%   $181.9451   $181.95   $181.95   $181.90  
  7 purchase totals = $974.39       $1,051.8415   $1,051.84   $1,051.80   $1,051.80