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 $154.33   13.812%   $175.6461   $175.65   $175.65   $175.60  
  Purchase #2 $129.28   12.110%   $144.9358   $144.94   $144.95   $144.90  
  Purchase #3 $210.86   5.631%   $222.7335   $222.73   $222.75   $222.70  
  Purchase #4 $66.95   4.672%   $70.0779   $70.08   $70.10   $70.10  
  Purchase #5 $181.31   11.171%   $201.5641   $201.56   $201.55   $201.60  
  Purchase #6 $56.68   5.751%   $59.9397   $59.94   $59.95   $59.90  
  Purchase #7 $225.58   9.222%   $246.383   $246.38   $246.40   $246.40  
  7 purchase totals = $1,024.99       $1,121.2801   $1,121.28   $1,121.35   $1,121.20